Best Open Source Team Chat Software in 2026
Self-hosted, source-available Slack alternatives you can run on your own servers, with no per-seat license required.
Mattermost and Rocket.Chat are the most mature, MIT-licensed self-hosted Slack alternatives, with no user cap on the free tier. Zulip organizes conversations by topic instead of noisy channels, and Element runs on the encrypted, federated Matrix protocol. Beyond those four dedicated chat tools, Nextcloud and Huly fold team chat into a broader open-source suite, Wire adds security-first messaging, and Jami drops the server entirely with peer-to-peer encryption. Every pick here ships real, auditable source code you can run yourself.
Most "open source Slack alternative" roundups mix in freemium SaaS products that just happen to have a generous free plan. That is not the same thing as open source: a proprietary chat app can shut off your workspace, raise its price, or get acquired at any time, and you have no recourse. From the 10,000+ tools Toolradar tracks, these are the open-source team chat and messaging platforms you can self-host as a Slack alternative: software with a public repository, a real license (MIT, Apache 2.0, AGPL, GPL, or EPL), and a working self-host path you control end to end.
We started from Toolradar's team chat and messaging categories, then verified each candidate's license and self-hosting instructions directly against its GitHub repository and documentation in 2026, dropping every tool that turned out to be closed-source SaaS with just a self-hosted deployment option. What is left spans three real models: dedicated chat servers (Mattermost, Rocket.Chat, Zulip, Element, Wire, CircleChat), team chat bundled into a broader open-source suite (Nextcloud, Huly), and a fully peer-to-peer messenger with no server at all (Jami). Every one of the nine has public source code, an active repository, and a genuinely free way to run it yourself.
Top Picks
Based on features, user feedback, and value for money.
| Tool | Starting price | Rating | Best for |
|---|---|---|---|
| Mattermost | From $10/mo | 4.3(596) | Engineering and DevOps teams that want channels, threads, and deep CI/CD integrations w... |
| Rocket.Chat | From $0.67/mo | 4.2(513) | Teams that want internal messaging and live customer chat running on the same self-host... |
| Zulip | Free plan | 4.8(308) | Distributed, async-first teams that need to catch up on days of conversation without sc... |
| Element | From $5/mo | 4.5(10) | Privacy-focused or multi-organization teams that need encrypted chat and the option to... |
| Wire | Free plan | 4.4(128) | Security-conscious teams, legal, or government-adjacent organizations that want end-to-... |
| Nextcloud | From $6.25/mo | 4.5(605) | Teams already self-hosting Nextcloud for files and docs that want to add chat and video... |
| Huly | From $19.99/mo | n/a | Small teams that want Slack-style chat and Jira or Linear-style project tracking in a s... |
| CircleChat | From $29/mo | n/a | Small technical teams that want a free, self-hosted chat app with channels and threads... |
| Jami | Free | n/a | Small teams or individuals who want encrypted messaging and calls without running, patc... |
Engineering and DevOps teams that want channels, threads, and deep CI/CD integrations without a per-seat SaaS bill.
Mattermost's pricing is fair, offering a generous Free tier for small teams.
Watch out
Self-hosting requires infrastructure costs
Teams that want internal messaging and live customer chat running on the same self-hosted platform.
Rocket.Chat's pricing is quite fair, especially for its open-source nature.
Watch out
Pro tier requires annual commitment
Distributed, async-first teams that need to catch up on days of conversation without scrolling one unbroken channel.
Zulip's pricing is quite fair and competitive, especially with a generous free tier.
Watch out
No annual discount mentioned, monthly billing only.
Privacy-focused or multi-organization teams that need encrypted chat and the option to federate across separate servers.
Element's pricing is very fair and generous, especially with a robust free tier offering unlimited messages and E2EE.
Watch out
Enterprise pricing is custom, potentially high.
Security-conscious teams, legal, or government-adjacent organizations that want end-to-end encrypted team chat with an auditable, self-hostable server.
Wire's pricing is fair, offering a generous free tier for personal use.
Watch out
Enterprise plan likely has minimum user count
Teams already self-hosting Nextcloud for files and docs that want to add chat and video calls without standing up a separate tool.
Nextcloud offers the best self-hosted cloud storage - completely free and open source.
Watch out
Server/hosting costs for self-hosted
Small teams that want Slack-style chat and Jira or Linear-style project tracking in a single self-hosted tool instead of stitching two products together.
Huly's pricing is quite generous, especially with its robust free 'Common' tier offering unlimited users and Huly Objects.
Watch out
AI features are 'TBD', potentially extra cost.
Small technical teams that want a free, self-hosted chat app with channels and threads where AI agents can act inside the same conversations.
The pricing is reasonable for niche AI-agent chat, with Starter at $29/mo for 3 agents being fair for small teams, but Team at $79/mo for only 10 agents is expensive compared to Slack or Teams that offer unlimited agents.
Watch out
No per-user billing; all seats tied to workspace
Small teams or individuals who want encrypted messaging and calls without running, patching, or paying for any server infrastructure.
Jami's pricing is exceptionally generous, offering a fully-featured, end-to-end encrypted communication platform completely free of charge.
Watch out
No hidden costs; truly free.
Other Team Chat worth considering
Beyond the editorial top picks, these are also strong choices we evaluated.
What Is an Open Source Team Chat Tool?
An open source team chat tool ships its source code under a license like MIT, Apache 2.0, AGPL, GPL, or EPL, so anyone can read it, audit it, modify it, and run their own copy on their own infrastructure. That is different from a proprietary tool that merely offers an on-premise or "self-hosted" deployment option: the binary is still closed, you still need a vendor-issued license key, and the vendor can still change the terms whenever it wants.
Not every open source pick in this guide works the same way. Some, like Mattermost and Zulip, are dedicated chat servers you deploy purely for messaging. Others, like Nextcloud and Huly, fold team chat into a broader open-source suite alongside files, docs, or project tracking, so one deployment gives you chat plus other tools. Jami skips servers entirely and connects devices peer-to-peer. Picking the right deployment model matters as much as picking the right license.
Why Self-Hosting Your Team Chat Matters
Self-hosting puts your message history, file uploads, and admin controls inside your own network instead of a third party's cloud. For regulated industries, government contractors, or privacy-focused teams, that is often a compliance requirement, not a preference: data residency, air-gapped deployments, and full audit logs are only possible when you control the server.
It also removes vendor risk. A proprietary chat SaaS can raise prices, get acquired, or shut down with a few months' notice, forcing a disruptive migration. Open source software cannot be discontinued out from under you: even if the company behind it folds, the code and your self-hosted instance keep running, and a community fork can pick up development.
Key Features to Look For
MIT, Apache 2.0, AGPL, GPL, or EPL on the actual server and client code, not just a marketing page that says the product is open.
The free tier should run in Docker or on bare metal with no phone-home activation and no artificial user cap.
A way to keep parallel conversations organized instead of one flat, noisy stream that everyone scrolls through.
Native desktop and mobile apps, not just a browser tab, so the tool actually replaces Slack day to day.
Recent commits and releases. An unmaintained fork with known vulnerabilities is worse than no self-hosted chat at all.
Bots, incoming and outgoing webhooks, and API access so the tool plugs into your existing CI, ticketing, and alerting stack.
Mistakes to Avoid
- ×
Assuming a "self-hosted" badge means open source. Some vendors sell a self-hosted deployment of closed-source software, license key and all, and you cannot audit or fork it.
- ×
Deploying the free community or self-hosted edition without checking which features are actually gated behind a paid tier, then getting surprised when SSO or clustering is missing.
- ×
Skipping a backup and upgrade plan for the self-hosted database, since you are now responsible for the uptime a SaaS vendor used to handle.
- ×
Choosing a broader suite like Nextcloud or Huly for chat alone without realizing you are also signing up to run and patch the entire platform, not just the chat module.
- ×
Ignoring the license split between the client and the server: some apps that call themselves open source only open the client while the server stays closed.
Expert Tips
- →
Run the free self-hosted tier with your actual team for a real pilot before comparing paid Enterprise pricing; most teams under a few hundred people never need it.
- →
Check the GitHub commit history and open issues before committing, not just the marketing site. A project with no commits in over a year is a liability.
- →
Match the deployment model to your infrastructure appetite: a dedicated server like Mattermost or Zulip if you just want chat, a suite like Nextcloud or Huly if you want chat plus files or project tracking, or peer-to-peer Jami if you want to avoid running a server entirely.
- →
For compliance-heavy environments, confirm exactly which edition includes audit logs and data retention. That is almost always the paid tier, even on open-core tools.
- →
Budget for your own ops time: self-hosting trades a per-seat SaaS bill for the work of patching, backing up, and scaling the server yourself.
The Bottom Line
Mattermost and Rocket.Chat remain the safest starting points for a mature, MIT-licensed Slack alternative with no user cap, while Zulip and Element fit teams that need topic threading or encrypted federation. If you want chat bundled into a bigger open-source suite, Nextcloud and Huly cover that, and Jami is the pick if you would rather run no server at all. Of the 10,000+ tools Toolradar tracks, these nine are the ones that are actually open source, not just self-hosted SaaS wearing an open badge.
Frequently Asked Questions
What is the best free open-source alternative to Slack?
Mattermost and Rocket.Chat are the two most mature options: both are MIT-licensed, self-host for free with no user cap, and cover channels, threads, and direct messages. Zulip is the strongest pick for distributed, async teams since it organizes messages by topic instead of one flat channel feed, and Element adds end-to-end encryption on the Matrix protocol.
What is the difference between Element and Matrix?
Matrix is the open, decentralized communication protocol; Element is the flagship client and server distribution built on top of it. Element's app is Apache 2.0 licensed, and the Element Server Suite Community edition is a free, AGPLv3-licensed way to self-host your own Matrix server for up to about 100 users.
Is Nextcloud a real team chat tool, or just cloud storage?
Nextcloud started as self-hosted file sync, but its Talk module is a full AGPL-licensed chat, voice, and video system with channels, screen sharing, and end-to-end encrypted calls. It makes the most sense if your team is already self-hosting Nextcloud for files and docs and wants to add chat without a separate tool; if you only want chat, a dedicated tool like Mattermost is lighter to run.
What is Huly, and is it actually open source?
Huly is an open-source, EPL-2.0 licensed workspace that combines team chat with project tracking, docs, and video calls, positioned as an alternative to Slack, Linear, Jira, and Notion in one app. It is genuinely open source, with a public self-host repository and no license fee for running it on your own hardware, and it has grown to around 26,000 GitHub stars with active daily development.
Can I get open source team chat without hosting a server at all?
Jami is the option here: it is a GPLv3 messenger that connects devices directly, peer-to-peer, with no central server to install or maintain. It covers encrypted messaging, group video calls, and file sharing for free, but it does not have Slack-style channels, threads, or bot integrations, so it fits small teams that want zero infrastructure more than it fits a full team chat replacement.
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