A disclosure before anything else: this is published by one of the products on the list. So rather than asking you to trust a scoring rubric that mysteriously ranks the host first, this compares on things you can verify independently — language, database, conversation model, what's gated behind a paid tier — and says plainly where each option is the better pick.
There are five serious open source options. Everything else is either a Matrix client, an abandoned repo, or a product that publishes a repo without being meaningfully self-hostable.
The field at a glance
| Mattermost | Rocket.Chat | Zulip | Element | Fluid Chat | |
|---|---|---|---|---|---|
| Language | Go | JavaScript | Python | TypeScript | TypeScript |
| Database | Postgres/MySQL | MongoDB | Postgres | Postgres | Postgres |
| Model | Channels+threads | Channels+threads | Channels+topics | Rooms | Channels+threads |
| Voice / video | Yes | Yes | Integrations | Yes | No |
| Native mobile | Yes | Yes | Yes | Yes | No |
| Federation | No | Yes | No | Yes | No |
| Admin gated by tier | Some | Some | Some (cloud) | Some | None |
| Ops surface | Medium | Medium–large | Medium | Large | Small |
Details are summarised from each project's public documentation and change over time. Verify before committing — including the row about us.
Mattermost — the enterprise one
Go on the backend, Postgres underneath, a long deployment history in serious organisations, and the compliance story to match. If your evaluation includes the phrase “procurement review,” Mattermost is probably where this ends.
- Best at: large regulated deployments, SSO/SAML, compliance exports, high availability, commercial support with a phone number.
- Watch for: open-core pricing. The features that matter at organisational scale live in paid tiers, so “free” has a follow-up question attached.
- Also has: playbooks and boards, which some teams love and others never open.
Deployment is a single Go binary plus Postgres, which is genuinely pleasant. At scale, search commonly moves to Elasticsearch, which adds a service.
Rocket.Chat — the everything one
Chat, voice, video, screen sharing, omnichannel customer support, an app marketplace and Matrix federation, all in one deployment. Nothing else in open source has this breadth.
- Best at: teams that need calls and customer-facing channels in the same product as internal chat. If you're running support over WhatsApp and web chat, this is close to unique.
- Watch for: MongoDB, which is a real operational commitment if your team's muscle memory is SQL. Also the free-tier terms, which have been revised more than once.
- Also has: the largest surface area on this list, which cuts both ways.
Zulip — the well-designed one
Python and Postgres, with the most genuinely interesting idea in the category: every message belongs to a named topic inside a channel, so catching up on a busy channel means reading coherent conversations rather than an interleaved mess.
- Best at: async teams across timezones, and open source communities where people need to catch up on three days without reading three days.
- Watch for: adoption. Topics require every person to name conversations as a habit. Teams that take to it become evangelists; teams that don't drift back to whatever they used before.
- Also has: an excellent free Cloud policy for open source projects, academic groups and some non-profits.
Element / Matrix — the federated one
Element is a client for Matrix, an open federated protocol. That's a different kind of product from everything else here: you're adopting a network, not just an app.
- Best at: federation across organisations, end-to-end encryption by default, and environments where protocol independence is a requirement rather than a preference.
- Watch for: operational weight. Running a Matrix homeserver well is the heaviest commitment on this list, and encrypted-history and device-verification UX has historically been the rough edge.
Fluid Chat — the small one
This is us, so treat the enthusiasm accordingly. TypeScript and Postgres, channels and threads, and a deliberate decision to do team messaging completely rather than a communications platform partially.
- Best at: the smallest operational surface (one database, three processes), and no feature tiers — audit logging, retention policies, guest scoping, scoped API keys and full export are all in the free product.
- Watch for: the scope limits. No huddles, voice or video. No SSO/SAML. No native mobile apps. No federation. No Slack importer yet, which is the most common dealbreaker.
- Also has: a free hosted version with no seat count and no history limit, if you'd rather not run anything at all.
How to actually choose
Skip the feature matrices and answer four questions in order. The first one that returns a strong answer decides it.
- 1Do you need voice, video or calls in the same tool? Yes → Rocket.Chat or Mattermost. This eliminates Fluid entirely.
- 2Do you need SSO/SAML or a compliance story? Yes → Mattermost.
- 3Is your real problem that busy channels are unreadable? Yes → Zulip. Nothing else solves this.
- 4Do you need federation across organisations? Yes → Element/Matrix.
If you answered no to all four, you're in commodity territory, and the deciding factors become operational: which database do you already run well, how many services do you want to babysit, and whether anything is gated behind a tier. That's the case Fluid is built for.
The head-to-heads
Evaluate the small one in two minutes.
Clone the repo and run docker compose up, or start a free hosted workspace. Then go and try at least one of the others — genuinely, that's how you'll know.
One thing all five get right
Every option here removes the 90-day history wall and the per-seat multiplier, which are the two reasons most teams start looking in the first place. The differences above matter, but they're second-order — if you're coming from a metered free plan, all five of these are an improvement, and the failure mode isn't picking the wrong one, it's spending four months picking.