At a glance — how these 6 alternatives compare
Our read on each project's adoption, maintenance activity and commercial-use risk, derived from GitHub signals and SPDX license terms rather than star count alone. Sorted by stars. How we score.
| Project | Adoption | Maintenance | Commercial use |
|---|---|---|---|
| ★ 45,680 · TypeScript | Flagship | Active | Unknown risk No clear SPDX id — treat as all-rights-reserved until verified |
| ★ 45,193 · TypeScript | Flagship | Active | Unknown risk No clear SPDX id — treat as all-rights-reserved until verified |
| ★ 38,093 · TypeScript | Flagship | Active | Unknown risk No clear SPDX id — treat as all-rights-reserved until verified |
| ★ 25,382 · Python | Mainstream | Active | Low risk Embed in a proprietary product with no copyleft obligation |
| ★ 13,228 · TypeScript | Mainstream | Active | High risk Even a hosted/modified deployment can trigger source release |
| ★ 2,330 | Established | Maintained | Unknown risk No clear SPDX id — treat as all-rights-reserved until verified |
The alternatives
Rocket.Chat
The Secure CommsOS™ for mission-critical operations
RocketChat/Rocket.Chat Updated 2026-06-20 Rocket.Chat
The Secure CommsOS™ for mission-critical operations
rocketchat/Rocket.Chat Updated 2026-04-23 mattermost
Mattermost is an open source platform for secure collaboration across the entire software development lifecycle..
mattermost/mattermost Updated 2026-06-19 zulip
Zulip server and web application. Open-source team chat that helps teams stay productive and focused.
zulip/zulip Updated 2026-06-19 element-web
A glossy Matrix collaboration client for the web.
element-hq/element-web Updated 2026-06-19 discussions
Repository for miscellaneous repository management and discussions: https://github.com/revoltchat/revolt/discussions
revoltchat/revolt Updated 2026-02-16 Editor's take
Yusuke Morinaga · last revisited
The five chat projects below are sorted by a single question — do you want Slack, or do you want something better than Slack?
Replacing Slack splits into two camps that people constantly conflate. One camp wants Slack, but self-hosted — same channels, same DMs, same muscle memory, no monthly bill. The other camp was never that happy with Slack’s model and wants something deliberately different. The five projects below land in one camp or the other, and choosing across the divide is how teams end up with a tool nobody adopts. Pick your camp first.
”Slack but self-hosted”: Rocket.Chat and Mattermost
Rocket.Chat (45.3k stars, TypeScript, NOASSERTION) is the broadest
Slack-shaped replacement: channels, DMs, threads, audio/video, a big
integration surface, omnichannel support add-ons. It is the closest to “all
of Slack” — and that breadth is also its cost. The admin UI is large, and
upgrades genuinely need planning rather than a casual docker pull. Its card
license is NOASSERTION because the community edition and enterprise features
have split terms — read the LICENSE before commercial embedding.
Mattermost (36.8k stars, TypeScript, NOASSERTION) is the tighter,
developer-and-DevOps-focused option. Deep GitLab/GitHub integration, solid
self-hosting story, and a more contained feature set than Rocket.Chat — which
many teams experience as a feature, not a limitation. If your org is
engineering-heavy and you want Slack-like chat without Rocket.Chat’s surface
area, Mattermost is the one I would trial first. Same NOASSERTION /
split-license caveat applies.
”Something better than Slack”: Zulip and Element
Zulip (25.2k stars, Python, Apache-2.0) is the contrarian pick, and the one I would actually push teams to try even if they think they want Rocket.Chat. Its threading model is fundamentally different — every message lives under a named topic within a channel — and for teams drowning in Slack’s linear-channel noise, it is genuinely better, not just cheaper. The cost is that it does not feel like Slack on day one, so adoption needs buy-in. The upside: Apache-2.0, the cleanest license in this whole list, no enterprise- edition asterisk.
Element (13.1k stars, TypeScript, AGPL-3.0) is the pick when decentralisation and federation are the actual goal — it is the flagship client for the Matrix protocol, so different organisations running their own servers can talk across them, and end-to-end encryption is first-class. This is the right answer for cross-org collaboration or strong privacy requirements, and the wrong answer if you just wanted a private team chat — in that case you are taking on the operational weight of running a Matrix homeserver for benefits you may not need. AGPL-3.0; fine for self-hosting.
The fifth entry, and a note on duplicates
This list also surfaces Revolt (2.3k stars) which is below our usual production bar and aimed more at community/Discord-style chat than workplace Slack — I would not put a company on it yet. (You may also notice Rocket.Chat appears twice in the cards above; that is two casings of the same GitHub repo in the upstream data, not two products.)
The Slack feature with no clean replacement
Slack Connect — shared channels spanning two different companies — has no native equivalent in Rocket.Chat, Mattermost, or Zulip; you work around it with guest accounts or a shared instance. Element/Matrix is the only option here that solves cross-org chat properly, via federation. If external collaboration was a core Slack use case for you, that single requirement may decide the whole thing.
Comparison notes
Rocket.Chat self-hosted replicates most Slack channel and direct message features and supports audio and video calls, but its admin UI is complex and upgrades require careful maintenance planning. Mattermost is more narrowly scoped, targeting developer and DevOps teams with GitLab and GitHub integrations, but lacks Slack's breadth of third-party app integrations and its workflow builder automation. Neither alternative provides a native equivalent to Slack Connect for cross-organization channels — external collaboration requires separate workarounds.
Migration tips
- Export your Slack message history using Slack's workspace data export (available on paid plans) and import into Rocket.Chat using its Slack importer plugin before migrating users.
- Recreate your channel structure in Mattermost or Rocket.Chat before the user migration date to preserve institutional organization patterns.
- Audit your active Slack integrations and identify equivalents — most webhook-based integrations are portable, but Slack OAuth apps with custom flows must be rebuilt against the new platform's API.
Which alternative should you pick?
We don't believe in a single "best" answer here — the right project depends on your license constraints, team size, and tolerance for early-stage tooling. The 6 projects above each have a distinct profile. Use this decision tree:
- You want the most active community and the lowest risk of abandonment → Rocket.Chat. 45,680★ — the largest user base in this list, which usually means more StackOverflow answers, more plugins, and more deployment runbooks online.
- You ship commercial software and need to ship modified code without releasing source → zulip. Apache-2.0 licensed — modify and embed without copyleft obligations.
- You want a strong-copyleft project that resists vendor capture → element-web. AGPL-3.0 licensed — downstream forks must stay open, which is what some teams explicitly want.
License & commercial-use notes
For an open-source replacement the license often matters more than any single feature — it decides whether you can modify the project, embed it in a product, or offer it as a hosted service. Here is how the 6 projects on this page break down:
- Permissive (zulip) — MIT / Apache / BSD / ISC — modify and embed inside a commercial product with no copyleft obligation. The safest bucket for shipping in a proprietary codebase.
- Network copyleft (element-web) — AGPL / SSPL — the copyleft trigger extends to offering the software over a network, so a hosted deployment of a modified version can oblige you to publish your changes. Read the exact terms before building a paid hosted product on these.
- Unverified license (Rocket.Chat, Rocket.Chat, mattermost, discussions) — GitHub returned no clear SPDX id. Treat as all-rights-reserved until you read the project's LICENSE file directly — do not assume commercial use is permitted.
License fields come from the GitHub API's SPDX classification and can lag a relicense. The repository linked on each card is authoritative — confirm its LICENSE file before any license-sensitive deployment.
Maintenance health of these 6 projects
Of the 6 projects listed, 6 shipped at least one commit in the last 12 months. See how we rank for the full criteria and our self-hosting cost reality check, which apply across every comparison on this site.
Frequently asked questions
What does end-user adoption look like compared to Slack?
Expect a 1-2 week dip in productivity while users learn the new UI, especially for power users who rely on Slack keyboard shortcuts and integrations. The OSS alternatives below close most of the gap on core features but lag on polish (drag-and-drop interactions, mobile apps, mature search). Pilot with a single team first.
How do these 6 alternatives compare on maintenance health?
6 of 6 have shipped a commit in the last 12 months. At least one project here has 5,000+ GitHub stars, which usually correlates with sustained maintainership. Always check the last-pushed date in the cards above and read the latest 5 closed issues — those two signals together catch 80% of abandoned-project cases.
How this page was compiled
- Repository facts (stars, license, language, last commit) come straight from the GitHub public API and are linked on each card as the primary source.
- Editorial analysis is drafted from Slack's use case and the alternatives' repository metadata, then reviewed by hand.
- Maintenance signal: 6 of 6 projects shipped a commit in the last 12 months as of the latest rebuild (most recent activity: ).
- Last editorial review: by Yusuke Morinaga.
- Spotted an error? Email [email protected] with the page URL (subject prefix
[correction]) — we ship corrections within 14 days.