slack alternative open source

published on 16 December 2023

Finding a free, open source alternative to popular team chat tools like Slack can seem daunting.

But there are viable self-hosted solutions that provide comparable features at no cost while giving you full control and customizability.

In this post, we'll explore leading open source Slack alternatives like Mattermost, Rocket.Chat, and Zulip - assessing their capabilities, scalability, and ease of use. We'll also provide guidance on choosing and implementing the right platform for your needs, helping you embrace the future of team communication with confidence.

Introduction to Open Source Team Chat Software

Why Seek a Free Slack Alternative?

Slack is a popular proprietary team chat and collaboration platform used by many businesses and teams. It offers features like threaded conversations, video calling, file sharing, integrations with other apps, and more. However, Slack is not free - pricing starts at $8 per active user per month for the Standard plan. For some small teams and organizations, particularly in the open source community, this ongoing cost may be prohibitive.

Additionally, some users may want more customization, flexibility, transparency, and control than Slack offers in its hosted commercial plans. As closed source software, Slack's code is not publicly visible for security audits. Some desire an alternative that aligns better with open source values.

Defining Open Source Software

Open source software has source code that anyone can inspect, modify, and enhance. It encourages collaborative development and community-driven support. The flexibility of open source allows customizations that aren't possible with proprietary alternatives. Enthusiasts argue it also enables more trust and transparency.

Benefits of Using an Open Source Slack Alternative

Potential benefits of using an open source Slack alternative include:

  • Cost savings - Avoid monthly fees in favor of free, open source options
  • Customizability - Code can be modified to add or tweak features
  • Privacy and security - Options for self-hosting instead of 3rd party servers
  • Community support - Decentralized teams collaborating on development and troubleshooting

Open source projects may lack some polish compared to paid tools, but can fulfill core team chat needs while aligning with values like transparency, flexibility and privacy.

Is there a free Slack alternative?

Yes, there are several popular free and open source Slack alternatives.

One commonly recommended option is Mattermost, an open source team chat platform. Mattermost offers many similar collaboration features as Slack, including public/private channels, direct messaging, emoji reactions, file sharing, search, and integrations. Some key benefits include:

  • Completely free and open source under an MIT license
  • Available to self-host on your own servers
  • Offers enterprise add-ons like video meetings, SSO, and analytics
  • Customizable to your needs with plugins and theming

Another alternative is Zulip, an open source team chat software focused on streamlining workflow through threaded conversations. Key features:

  • Open source software with hosting options
  • Unlimited users, messages, and integrations on self-hosted version
  • Topic-based threading keeps conversations contextual
  • Powerful filtering, muting, and notification settings

Additionally, Rocket.Chat provides a customizable open source Slack-like platform for internal communications. It supports unlimited users on self-hosted options.

In summary, Mattermost, Zulip, and Rocket.Chat are highly capable free and open source alternatives to Slack that offer self-hosting flexibility. They provide reliable platforms for team messaging, collaboration, and chat communications with customizable options to fit your needs.

Is there an open-source Slack?

Mattermost is an excellent open-source alternative to Slack that offers similar features and functionality. As an open-source team chat platform, Mattermost provides:

  • Secure messaging across web, desktop, and mobile apps
  • File sharing, search, and integrations with other tools
  • Public, private, and direct messaging channels
  • Video calling and screen sharing
  • Custom theming and branding options

Mattermost is self-hosted, so you have full control and ownership over your data. Since anyone can freely use, modify, and distribute the source code, Mattermost benefits from continuous community contributions and improvements.

Some key advantages of using the open-source Mattermost over Slack include:

  • No vendor lock-in - export data anytime
  • Enhanced security and compliance
  • Lower total cost of ownership
  • On-premises deployment flexibility
  • Private cloud or self-hosted options
  • Unlimited messaging history
  • Wider range of integrations

For teams that want an affordable, flexible, and highly capable team chat system, Mattermost delivers enterprise-grade capabilities as a free open source alternative to Slack.

Does Google have a Slack alternative?

Google offers Google Chat as a free alternative to Slack for businesses using Google Workspace. Formerly known as Hangouts Chat, Google Chat provides team messaging, video meetings, and integrates tightly with other Google services like Drive and Docs.

Some key things to know about Google Chat:

  • Completely free with a Google Workspace account
  • Supports direct messages, group chats, threaded conversations
  • Video calling support through Google Meet integration
  • File sharing and real-time collaboration with Google Drive
  • Available as web, desktop, and mobile apps
  • Customizable notifications and Do Not Disturb modes
  • Third-party integrations with other apps via bots
  • Lacks some advanced Slack features like Workflow Builder

For teams already using Google Workspace, Google Chat can be a compelling free alternative to explore instead of paying for Slack. The tight integration with Google's other productivity apps makes it easy to chat, collaborate, and have meetings without switching contexts.

While more fully-featured, Slack may still be preferable for larger teams that need more customization. But Google Chat covers the basics well and its continuing development may close the gap over time. For small teams, it's definitely worth considering as a free and convenient team chat option.

What will replace Slack?

As collaboration tools like Slack gain popularity, some organizations are seeking open source alternatives that offer more flexibility, customization, and control over their communications. Mattermost is one such open source option that provides Slack-like team messaging and productivity features.


Mattermost offers core capabilities like group chat, file sharing, search, and integrations with popular apps. As an open source platform, Mattermost provides the underlying source code so enterprises can run the software on their own infrastructure. This allows them to host data internally rather than relying on a third-party cloud.

Other major features include:

  • Video and voice conferencing
  • Customizable interface
  • Secure communications
  • Mobile apps
  • Bots and workflow automations
  • Native cross-platform support
  • LDAP/AD and SSO authentication

Benefits Over Slack

Choosing Mattermost over Slack provides certain advantages:

  • Lower Cost: Mattermost is free open source software with no per-user fees. Organizations only pay for hosting infrastructure.
  • Data Control: Sensitive information stays on-premises rather than a vendor's cloud.
  • Customizability: Mattermost allows deep customization to tailor workflows.
  • No Vendor Lock-in: Mattermost is not dependent on a single vendor's technology decisions or pricing models.

For teams that value control, privacy, and flexibility, Mattermost presents a compelling self-hosted alternative to popular hosted services like Slack. Its focus on enterprise needs makes it a leading contender to replace Slack across security-conscious organizations.


Exploring Open Source Slack Alternatives

This section provides an overview of some popular open source chat platforms that can serve as alternatives to Slack.

Mattermost: A Comprehensive Self-Hosted Slack Alternative

Mattermost is an open source, self-hosted online chat service designed as an internal chat system for teams. It aims to provide a Slack-alternative with enterprise-grade security and compliance.

Some key features of Mattermost include:

  • Platform Support: Available on Linux, macOS, Windows, Kubernetes
  • Messaging: Public/private channels, direct messages, file sharing
  • Search: Fast search with filters and wildcards
  • Integrations: 1800+ third-party integrations and APIs
  • Desktop/Mobile Apps: iOS, Android, Windows, macOS
  • Security: SAML, LDAP, HTTPS, Hosted option

As Mattermost is self-hosted, organizations have complete data ownership and operational control. It can be deployed on-premises or via cloud platforms like AWS, Azure, Docker.

The pros of Mattermost are its rich capabilities, compliance standards, data security/control. The cons are the expertise needed for setup/management, lack of full UX feature parity vs Slack.

Overall, for teams needing an open-source, self-managed alternative to Slack, Mattermost checks all the boxes.

Rocket.Chat: An Extensible Open Source Team Chat Software

Rocket.Chat is a free open source team chat solution similar to Slack. Some distinct features include:

  • LiveChat: Customer engagement/support integration
  • Audio/Video Chat: Built-in conferencing options
  • Bots Framework: Create custom chatbots
  • Themes: High customization and theming
  • Mobile SDKs: iOS, Android, React Native

It can be deployed on cloud platforms like AWS, Azure, Heroku or self-hosted.

Comparing Rocket.Chat to Mattermost - while Mattermost edges out on security and compliance features, Rocket.Chat provides more extensibility, custom bots/apps and UI personalization.

So Rocket.Chat appeals to teams wanting an open framework to build customized workflows. But Mattermost better serves regulated enterprises.

Zulip: Stream-Based Open Source Team Communication

Zulip takes a unique approach to team chat with topic streams, instead of channels. Each stream has topics associated with it. This allows threaded conversations neatly separated by subject, great for globally distributed teams.

Zulip streams tend to be long-lived, persistent communication forums. While more chatty conversations suited to Slack channels happen in private or group messages.

Other capabilities include:

  • Integrations: Github, Jira, Jenkins and more
  • Search: Powerful full-text search
  • Mobile apps: Android, iOS
  • Self-hostable and managed cloud options

So Zulip brings new ideas on structuring team conversations for productivity. The stream/topic model aligns well for software teams to track projects, issues, PRs. For other teams, its usefulness varies.

Comparing Mattermost vs Slack

Feature Set Comparison

Mattermost and Slack have similar core functionality for team messaging and collaboration, including public/private channels, direct messaging, file sharing, search, and integrations. However, Mattermost offers more extensibility and control while Slack provides a more polished user experience out of the box.

Key differences in features:

  • Mattermost enables creating custom workflows with JavaScript and Golang plugins. Slack has an app directory but less customizability.
  • Mattermost offers native video calling. Slack requires integrating a third-party tool like Zoom.
  • Slack has better interfaces and comes with more predefined slash commands. Mattermost enables building custom slash commands.
  • Mattermost can be self-hosted on a private cloud or data center. Slack is proprietary SaaS without on-premises options.

Both services cover the basics like notifications, @mentions, threaded conversations, emojis, Markdown support etc. Slack has more features for non-technical teams while Mattermost caters more to developers and IT teams.

Cost Analysis: Mattermost Open Source vs Slack Pricing

As open source software, Mattermost can be deployed without any license fees on the user's infrastructure. The Enterprise Edition adds advanced security, compliance and automation capabilities for a per-user annual subscription.

Slack follows a freemium model, offering limited features for free and expanded capabilities on their Standard, Plus or Enterprise Grid plans, charged per user per month.

This means Mattermost can provide immense cost savings for self-managed deployments, especially at scale. However, hosting and maintaining the Mattermost infrastructure requires IT resources and skills. Slack offers convenience but the costs ramp up with more users and features.

Deployment and Self-Hosting Capabilities

Mattermost is designed for flexible self-hosted deployments on a private cloud like AWS, data centers, or on-premises servers. It supports both cloud-native Kubernetes installations as well as single-machine deployments.

In contrast, Slack is proprietary SaaS without self-hosted or on-premises options. User data and conversations stay within Slack's cloud platform rather than an organization's own infrastructure.

This allows Mattermost to meet strict data sovereignty and residency laws in some regulated industries. It also gives organizations direct control, customization and oversight of the collaboration solution. However, the self-hosted model requires hands-on system administration and DevOps skills.

Community Support and Development

As open source software, Mattermost relies on community contributors for development, testing, documentation and support through public channels like forums, GitHub, and Stack Overflow. Critical security issues can receive dedicated Enterprise Edition support services.

Slack invests heavily in refining user experience with an internal team of designers and engineers. It offers official customer support and SLAs for uptime and responsiveness. However, there is less transparency into Slack's feature roadmap.

With Slack, users depend on the vendor's vision. Mattermost gives organizations more influence in driving development priorities for the self-hosted application. But open source community support varies and typically lags dedicated commercial support services.

Selecting the Right Self-Hosted Slack Alternative

Assessing Intended Use Cases for Team Chat

When evaluating a self-hosted Slack alternative, first consider your intended use case and communication needs. Are you looking to enable chat primarily for internal team collaboration? Do you need extensive integrations with other workplace apps? Will guests or external communities take part in conversations? Understanding the use case will help narrow down options.

For example, Mattermost and Rocket.Chat excel for internal discussion and workplace project management chat. Discourse may be preferred for public community building. Analyzing the user base, content types, integrations, and chat features needed will clarify the ideal fit.

Technical Expertise for Setup and Management

The technical expertise required should also factor into selecting self-hosted team chat software. Platforms like Mattermost, Rocket.Chat offer 1-click install options, while options like Zulip or Matterbridge may demand more hands-on configuration and Linux server skills.

Review available documentation, pre-configured developer environments for testing, and activity levels of community tech support channels. Assess if your staff resources can sustain ongoing software, security and integration management after the initial setup as well.

Evaluating Scalability and Performance Needs

Consider your organization's size and projected growth when assessing self-managed Slack alternatives. Mattermost and Rocket.Chat offer enterprise plans to scale up to large deployments elegantly. Other options may suffice for smaller teams willing to work within more limited capacity thresholds before performance degrades.

Testing options under heavy simulated workloads is advised to validate they can handle peak demand reliably while cost-effectively utilizing infrastructure resources. Often scaling chat servers presents distinct resource and high-availability challenges from web servers.

Compatibility with Mobile and Desktop Platforms

Cross-platform accessibility across devices is pivotal for chat utility. Mobile compatibility may increasingly be a priority to enable communication from anywhere.

Assess mobile app Store availability, ratings and feature support for each platform, along with native desktop app options. While web access suffices for some, native OS integration drives more seamless notifications and faster access on the go. Support breadth, app stability and multi-device sync should factor into mobile evaluation.

Integrating with Existing Workplace Tools

If third-party integrations are essential, review the extension ecosystems of each platform carefully early on. While all leading options today offer some integration capabilities, breadth and ease of linking chat conversations into common workplace tools like Jira, GitHub, Trello etc. can vary greatly.

Prioritize must-have tools for workflows, evaluating extensibility options or even feasibility of custom integration development per platform. This will prevent integration gaps from negating other benefits later.

Implementation Strategies for Open Source Team Chat

Securing Leadership Buy-In for Open Source Solutions

Transitioning from a proprietary chat platform like Slack to an open source alternative like Mattermost involves upfront investment of money, time, and effort. To secure leadership approval, the benefits of open source team chat must be clearly communicated:

  • Cost savings: Self-hosting eliminates recurring licensing fees. Long term TCO is lower.
  • Data ownership: Full control over all communications data and chat history. No vendor lock-in risk.
  • Customizability: Tailor the platform to organization's unique needs and preferences with open code.
  • Security: On-premise deployment enables advanced security configurations not possible with SaaS tools.
  • Community: Tap into active open source community for troubleshooting help and feature requests.

Prepare a detailed cost analysis highlighting the return on investment over 3-5 years from migrating. Pitch it as an opportunity to prevent vendor lock-in and take back ownership of your digital workspace.

Facilitating User Onboarding and Training

Smoothly transitioning end users to the new Mattermost platform is critical for driving adoption. Recommended strategies include:

  • Gradual rollout: Slowly migrate departments in phases to allow proper onboarding over weeks/months.
  • Personal training: One-on-one walkthroughs of Mattermost interface and features builds confidence for switch.
  • Quickstart guides: Create customized user manuals, cheat sheets, video tutorials to facilitate ramp up.
  • Power users: Identify chat power users across departments to provide peer training and support.

Make self-service support resources readily available. Proactively seek user feedback during the transition to quickly resolve pain points.

Fostering Engagement and Collaboration

To encourage active daily use of Mattermost for enhancing teamwork, productivity, and alignment across the organization:

  • Gamification: Apply points/badges for usage milestones to motivate engagement.
  • Automations: Build custom integrations with key business systems to centralize notifications and workflows.
  • Showcases: Host quarterly seminars for teams to demonstrate how they creatively use Mattermost to collaborate.
  • Exec buy-in: Get leadership to commit to conducting daily standups and meetings in Mattermost chat rooms.

Promote channel creation aligned to processes, projects, interests etc. to unify communications.

Leveraging Analytics and User Feedback

Gain actionable insights into platform traction and experience by:

  • Monitoring usage over time with daily/monthly active user dashboards segmented by team, role, etc.
  • Surveying early user cohorts on what features they find most/least valuable.
  • Tracking most popular integrations and embedded apps to guide future customizations.
  • Sending NPS surveys periodically to benchmark user satisfaction/adoption challenges.

Create centralized feedback channels for users to easily submit bug reports and feature requests. Rapidly implement quick fixes and improvements based on usage analytics and user input.

Conclusion: Embracing the Future of Team Communication

As we have seen, open source alternatives like Mattermost offer a compelling option for organizations looking to improve team communication and collaboration. By switching from proprietary tools like Slack, companies can benefit from greater customization, data ownership, and cost savings.

Here are some key takeaways:

  • Open source team chat platforms provide the flexibility to host your own data and integrate deeply with your existing stack. This allows for more customization to meet your specific needs.
  • Avoiding vendor lock-in through open source software gives you more control over your team communication system long-term. You are not tied to a single vendor's pricing plans or changes.
  • The availability of self-hosted open source alternatives removes recurring license fees, allowing large teams and organizations to save significantly on costs.
  • Active open source communities enable faster innovation and addition of new features compared to proprietary tools. Patches and fixes can be implemented quicker as well.
  • For developers already working extensively with open source software, staying within the open source ecosystem results in a more seamless and efficient workflow.

As teams grow rapidly in the remote-first future of work, selecting a future-proof communication and collaboration platform is key. Open source alternatives offer the flexibility, security, and cost structure required by many modern organizations. By investing time upfront in research and testing, teams can benefit greatly in the long run after a successful transition to platforms like Mattermost.

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