At a glance — how these 4 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 |
|---|---|---|---|
| ★ 46,225 · TypeScript | Flagship | Active | Low risk Embed in a proprietary product with no copyleft obligation. Split licence — this rates the core component; read the † text for the separately licensed parts |
| ★ 39,292 · TypeScript | Flagship | Active | High risk Even a hosted/modified deployment can trigger source release. Split licence — this rates the core component; read the † text for the separately licensed parts |
| ★ 26,013 · Python Apache-2.0 | Mainstream | Active | Low risk Embed in a proprietary product with no copyleft obligation |
| ★ 13,547 · TypeScript AGPL-3.0 | Mainstream | Active | High risk Even a hosted/modified deployment can trigger source release |
† Licenses marked † were read from the repository's LICENSE file on 2026-09-05 (linked, pinned to the commit we read) because the GitHub API returned no SPDX id for them. Unmarked licenses are the GitHub API's SPDX classification.
The alternatives
The Secure CommsOS™ for mission-critical operations
RocketChat/Rocket.Chat Updated 2026-10-08 Mattermost is an open source platform for secure collaboration across the entire software development lifecycle..
mattermost/mattermost Updated 2026-10-08 zulip
Zulip server and web application. Open-source team chat that helps teams stay productive and focused.
zulip/zulip Updated 2026-10-08 element-web
A glossy Matrix collaboration client for the web.
element-hq/element-web Updated 2026-10-08 Editor's take
Yusuke Morinaga · last revisited · star counts quoted in the text (≈) are as of that date; the cards above are refreshed daily
The four 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 four 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 (≈46.1k★, TypeScript, MIT core) 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. The
GitHub API returns no SPDX id for it because the community edition and
enterprise features have split terms; the card shows what we read in the
repository’s LICENSE — MIT for everything outside apps/meteor/ee/ and ee/.
Read the LICENSE before commercial embedding.
Mattermost (≈39k★, TypeScript, AGPL-3.0 or commercial) is the tighter, developer-and-DevOps-focused option. Deep GitHub/GitLab integrations, 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. The same split-licence caveat applies: the GitHub API returns no SPDX id, and the LICENSE we read puts the source under AGPL-3.0 or a commercial licence, the webapp, public server packages, templates and i18n under Apache-2.0, and compiled builds under MIT.
”Something better than Slack”: Zulip and Element
Zulip (≈25.8k★, 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 (≈13.4k★, 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 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?
Replacing Slack isn't a single call — it's a trade between license terms, team size, and how much early-stage roughness you can absorb. The 4 projects above split along those lines:
- You want the project with the most GitHub stars in this list → Rocket.Chat. 46,225★ — the most of the 4 projects here. Stars measure attention, not quality or maintenance; check the last-push date and the Editor's take before reading more into it.
- 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 copyleft project whose modifications must be shared back → element-web. AGPL-3.0 licensed — distributing a modified version (and, under AGPL, offering it over a network) obliges releasing the source, which is what some teams explicitly want.
- You want the project with the most recent push activity → zulip. Last push 2026-10-08 — the freshest activity in this list.
License & commercial-use notes
When replacing Slack, the license usually decides more than the feature list — whether you can modify it, ship it inside a product, or host it as a service. The 4 projects here fall into:
- Permissive (Rocket.Chat, 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 (mattermost, 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.
Split licences: Rocket.Chat (MIT (core) + separate license for apps/meteor/ee/ and ee/); mattermost (AGPL-3.0 or commercial license (source) + Apache-2.0 (webapp/, server/public/, templates, i18n) + MIT (compiled builds)). These projects are grouped above by the core licence; the separately licensed directories (enterprise or EE parts) are not covered by that bucket — check which files you actually ship.
License fields come from the GitHub API's SPDX classification and can lag a relicense. Where the API returned no SPDX id, the license marked † was read from the repository's LICENSE file on 2026-09-05; the † links to the exact file and commit we read. The repository linked on each card is authoritative — confirm its LICENSE file before any license-sensitive deployment.
Maintenance health of these 4 projects
Of the 4 projects listed, 4 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
How do these 4 alternatives compare on maintenance health?
4 of 4 have shipped a commit in the last 12 months. At least one project here has 5,000+ GitHub stars. Always check the last-pushed date in the cards above and read the latest closed issues — those two signals are the fastest public check we know of.
How this page was compiled
- Repository facts (stars, license, language, last push) come straight from the GitHub public API and are linked on each card as the primary source. Where the API returned no SPDX id, the licence marked † was read from the repository's
LICENSEfile (linked, pinned to the commit we read, with the date checked). - Editorial analysis (the intro, comparison notes and migration tips) is Claude-drafted from Slack's use case and the alternatives' repository metadata — in Claude Code sessions or scheduled routines run under the operator's account. Samples are spot-checked against the upstream repositories; entries are not individually reviewed unless they carry a signature. See what Claude drafts and what the operator writes.
- Editor's take is signed by Yusuke Morinaga. It was drafted in a Claude Code session the operator ran, then read and confirmed by Yusuke Morinaga before publication, and carries the date it was last revised. It is written from each project's README, LICENSE, release history and issue tracker — not from running the project in production; where that distinction matters, the take says so.
- Maintenance signal: 4 of 4 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.