Every company has a room where the real decisions get made, and for ten years that room has been rented by the message. Slack's free plan now hides anything older than 90 days and deletes it after a year, and the two open source projects people reached for instead have both put caps on their free editions this past year.
Zulip is what happens when someone decides the room should come with the building.
The best open source messaging platform to run yourself is Zulip for most teams: Apache-2.0, free to self-host with no user limit and, in its own words, “no open core catch”, and $6.67 a user a month on its cloud if you would rather not run it (checked Nov 7, 2026). Mattermost and Rocket.Chat are the closer Slack look-alikes, and both now ship a free edition with a user cap: Mattermost Team Edition at 250 users and Rocket.Chat Starter at 50. Matrix, through the Synapse server and the Element client, is the pick if you want federation between organisations rather than one company's chat.
What a free messaging platform costs now
Free team chat got smaller in the last eighteen months, at the proprietary end and the open source end alike. Slack's free plan keeps 90 days of message history visible and, since August 26, 2024, deletes customer data older than one year from free workspaces, per Slack's own help centre (checked Nov 7, 2026). The free plan also allows 10 app integrations and one workspace. From Europe, Slack's pricing page shows Pro at €8.25 a user a month billed monthly or €6.75 billed yearly, Business+ at €18 or €15, and Enterprise+ at €45 billed yearly.
Mattermost changed its free offerings with version 11 in October 2025. Its forum announcement says Team Edition, the MIT-compiled free build, drops GitLab SSO and lowers its user limit “from 1,000 to 250”, and introduces Mattermost Entry, a free edition under a commercial licence with the full feature set and rate limits (forum.mattermost.com, Aug 23, 2025). Rocket.Chat's docs now provision every new workspace as Starter, free for up to 50 users, and describe the MIT Community edition as capped at 100 concurrent users and 10,000 push notifications a month, “not suitable for production deployment” for organisations that depend on it (docs.rocket.chat, checked Nov 7, 2026). The code stayed open in both cases. The free build got a fence.
The open source messaging platforms did not close their code. They put a user count on the free binary, which is the one number a self-hoster used to be able to ignore.
The open source messaging platforms you can self-host
Of the 436 communication tools in the AppClap catalog (Nov 7, 2026), 113 are open source and 254 have a free tier. These four are the ones worth running as a team's main room.
Zulip
Zulip is team chat organised by topic inside each channel, so a busy stream reads like threads you can actually catch up on. Self-hosting is free with no user cap; the self-hosted Basic plan, which buys mobile push notifications past 10 users, is $3.50 a user a month, and Business is $6.67 a user a month billed annually with a 25-user minimum (checked Nov 7, 2026). Zulip Cloud has a Free plan with 10,000 messages of search history and a Standard plan at $6.67 a user a month billed annually, which the plans page says many organisations are eligible to get free. The licence is Apache-2.0, with about twenty-six thousand stars and version 12.4 out on Nov 6, 2026 (repo). It is best for a team that writes more than it talks. The honest drawback is that topics take a week to feel natural, and some people never get there.
Mattermost
Mattermost is the Slack look-alike for people who run their own servers: channels, threads, calls, playbooks and boards in a single Go binary on PostgreSQL. Team Edition is free, compiled under MIT, and limited to 250 activated users with no SSO (Mattermost docs, checked Nov 7, 2026). Mattermost Entry is also free, under a commercial licence, with every Enterprise Advanced feature and server-wide rate limits. Professional covers up to 250 users and the pricing page shows no price, only “prepaid annual subscriptions”. The open source project is AGPL-3.0 with about thirty-nine thousand stars, and version 12.0.2 shipped on Nov 4, 2026 (repo). It is best for a developer team that wants Slack's shape on its own hardware. The drawback is that both free editions are now fenced, and the paid price is a sales call.
Rocket.Chat
Rocket.Chat is the other full Slack replacement, with voice, video meetings and screen sharing built in. Every new workspace is a Starter workspace: free, self-hosted, up to 50 users, with most premium features under usage limits. Past 50 you either buy a Commercial, Government or Defense plan, which are quote-only on Nov 7, 2026, or downgrade to Community, the MIT edition capped at 100 concurrent users and 10,000 push notifications a month. The core is MIT with an enterprise folder under its own licence, about forty-six thousand stars, and version 8.9.1 out on Nov 6, 2026 (repo). It is best for a company that wants calls and screen sharing in the same tool as chat. The drawback is that Rocket.Chat's plans page no longer prints a price at all.
Matrix: Synapse and Element
Matrix is a protocol rather than a product, so you run a homeserver and pick a client. Synapse is the reference server, AGPL-3.0 under a dual licence from Element, with about forty-eight hundred stars on the current repository and version 1.164.2 released on Nov 2, 2026 (repo). Element is the main client, also AGPL-3.0 with about thirteen thousand six hundred stars for the web app. Element's own Server Suite Community edition is “free of charge frontend and backend” but marked “not for use in production environments”, and the Enterprise tier is “priced per seat/month” with no number shown (element.io, checked Nov 7, 2026). Conduit is another homeserver, written in Rust. Matrix is best when two organisations need to share rooms without sharing a server. The drawback is that encryption keys and federation are a second job for whoever runs it.
| Platform | Licence | Free self-hosted limit (Nov 7, 2026) | Published paid price |
|---|---|---|---|
| Zulip | Apache-2.0 | None | $3.50 to $6.67 a user a month |
| Mattermost Team Edition | MIT compiled, AGPL-3.0 source | 250 users, no SSO | None shown |
| Mattermost Entry | Commercial, free | Under 50 users, rate limits | None shown |
| Rocket.Chat Starter / Community | MIT core | 50 users / 100 concurrent | Quote only |
| Matrix (Synapse + Element) | AGPL-3.0 | None on the open server | Per seat, no number |
The AppClap flat-price test, where a tool passes when the price on its pricing page is the price on the invoice, has one clean pass among these vendors: Zulip, whose prices are printed and per user. Mattermost, Rocket.Chat and Element all ask you to talk to sales. Pumble is the proprietary oddity worth naming: its free plan covers unlimited users with unlimited message history, and Pro is $2.49 a seat a month billed annually (checked Nov 7, 2026). It is not open source, but it is the cheapest way to keep a Slack-shaped history without a server.
Is Mattermost free?
Yes, in two ways, and both now have limits. Mattermost Team Edition is free and open source, compiled under MIT, for up to 250 activated users without SSO. Mattermost Entry is free under a commercial licence, includes SSO and every enterprise feature, and carries server-wide limits that the docs list as 10,000 viewable channel messages, 1,000 board cards, 5 playbook runs a month, 250 agent queries a month, 40-minute calls and 10,000 push notifications a month, several marked as taking effect in a future release (Mattermost docs, checked Nov 7, 2026). The underlying open source project stays AGPL-3.0, and anyone can compile it without either fence, which the v11 announcement says explicitly. For a team under 50 people, Entry is the free version Mattermost now wants you to run.
Is Slack free for small teams?
Yes, with a 90-day window on what you can see and a one-year limit on what Slack keeps. Slack's free plan costs €0 on the European pricing page and allows 10 app integrations and one workspace, but only the last 90 days of messages and files are visible, and data older than a year is deleted on a rolling basis (Slack help centre, checked Nov 7, 2026). A team of five that never scrolls back is fine. A team that searches for last spring's decision is on Pro at €6.75 a user a month billed yearly.
What you actually take on
Slack earns its seat with the parts none of these projects have finished: a mobile app that never needs a server address, integrations that just work, Slack Connect channels with other companies, and a security team that is not you. Mattermost's and Rocket.Chat's paid plans sell the same relief to regulated industries, which is why their pricing pages now talk about air-gapped deployment rather than dollars.
Running your own messaging platform means you own uptime for the thing everyone opens first in the morning. You patch the server, back up the database, keep the push notification relay working, and when a certificate expires on a Saturday, the whole company goes quiet at once. Zulip charges self-hosters for exactly one thing past 10 users, mobile push notifications, which tells you where the work is. The honest middle is a maintainer's cloud: Zulip Standard at $6.67, or Element's and Mattermost's hosted tiers if you can get a quote.
- 1Do you have someone comfortable running a Linux server, a database and a push notification relay?
- 2Is your team under 50 people, so Mattermost Entry and Rocket.Chat Starter are free, or over, so only Zulip and Matrix have no cap?
- 3Does the message history actually matter, or is Slack's 90-day window fine?
- 4If chat goes down at 9am on a Monday, is that a problem you would rather own or outsource?
We keep circling this pattern at AppClap, because the whole job is helping you find the tool that actually fits, and “self-hosted” now needs a footnote about user caps. The reaper has worked down the hallway past dictation, deploys, the CRM, the front door, the task board and the team notebook, and today he is at the break room, where the conversation itself has a seat price. Spend thirty seconds on a self-hosted team chat with no user limit, browse the open source communication tools we track, and ask the question this series always ends on: do you want to rent the room, or own it?
Sources: slack.com, Pricing (as shown from Europe) and help centre articles “Usage limits for free workspaces” and “Feature limitations on the free version of Slack”; mattermost.com, Pricing; docs.mattermost.com, “Editions and Offerings”; forum.mattermost.com, “Mattermost v11 Changes in Free Offerings” (Aug 23, 2025); mattermost.com blog, “Introducing Mattermost Entry” (Oct 16, 2025); rocket.chat, Plans; docs.rocket.chat, “Our plans”; zulip.com, Plans and Self-hosting; element.io, Pricing; pumble.com, Pricing; GitHub repos zulip/zulip, mattermost/mattermost, RocketChat/Rocket.Chat, element-hq/synapse and element-hq/element-web; AppClap catalog counts, Nov 7, 2026. All checked Nov 7, 2026.
