What problem are you actually solving

Before picking software, be honest about what you want chat for. A private family or friend-group chat that just needs to not be owned by a tech company is a completely different problem from standing in for Slack at a small team or business, which is different again from wanting a federated, decentralized network you can bridge into other communities. All three tools can technically do all three jobs. Only one of them is actually good at each.

Matrix: the protocol, not just an app

Matrix is fundamentally different from the other two because it’s a federation protocol first, with Synapse (the reference server implementation) as the piece most people actually run. That distinction matters more than it sounds. Where Rocket.Chat and Mattermost are single-organization chat platforms you happen to self-host, Matrix is designed so your homeserver can talk to other people’s homeservers, the same way email servers federate, while still keeping your own data and your own moderation under your own roof.

The payoff is real: end-to-end encryption by default in private rooms, bridges to Discord, Telegram, Slack, IRC, and others that let you read and send messages in those networks from inside Matrix, and the ability to join public Matrix rooms hosted anywhere without needing an account on someone else’s server. The cost is also real. Synapse is notoriously heavy on both RAM and, more specifically, database load as room membership and message history grow, because federation means tracking a lot of state about rooms you don’t even control. A small private homeserver for a handful of people is fine on modest hardware. A Synapse instance that joins a lot of large public rooms, or that a wider community actually uses daily, is a different sizing problem entirely, and it’s the single most common complaint from people running it at home.

Lighter server implementations exist, Conduit and Dendrite being the two most talked about, trading some of Synapse’s feature completeness and federation robustness for a dramatically smaller footprint. They’re worth considering if your actual need is “small private chat with a handful of people” rather than “fully-featured server that plays well with the wider Matrix ecosystem,” but go in expecting rougher edges and slower-moving development than Synapse. Client-side, Element is the flagship app and the one most documentation assumes, with a handful of alternative clients if its UI doesn’t suit you.

Rocket.Chat: the omnichannel generalist

Rocket.Chat positions itself less as a Slack clone and more as a full customer-engagement platform that happens to include team chat: live chat widgets for a website, omnichannel support routing, video conferencing, and a long list of third-party integrations alongside the core messaging. If you specifically want a self-hosted chat widget for a small business site in addition to internal team chat, it’s genuinely one of the few self-hosted options built for that combined use case.

Operationally it runs on Node.js backed by MongoDB, and the MongoDB dependency is worth knowing before you commit, because real high-availability setups want a MongoDB replica set, not a single standalone instance, which adds a layer of database operations most homelabs don’t otherwise need to think about. For a single-instance homelab deployment this is a non-issue, just run one MongoDB container and move on, but it’s the reason Rocket.Chat feels like more moving parts than Mattermost for the same basic team-chat job. The admin panel is dense, reflecting how much the product actually does, which is a feature if you want the extra capability and friction if you just wanted a chat server.

Mattermost: the closest thing to a Slack clone

Mattermost is the most direct Slack lookalike of the three, both visually and in how it’s organized: teams, channels, threads, slash commands, and a plugin system that mirrors a lot of what Slack’s app ecosystem does. If your team already thinks in Slack’s mental model and you want to migrate off it with the least retraining, Mattermost is the smallest behavioral jump.

It ships as a single Go binary plus a Postgres (or MySQL) database, which makes it noticeably lighter to run and reason about than Rocket.Chat’s Node/MongoDB stack or a Synapse homeserver, and updates are generally straightforward. The free, self-hosted edition is genuinely usable as a daily driver for a small team, though some features you’d expect from Slack’s paid tiers, like certain compliance, SSO, and advanced administration options, are gated behind Mattermost’s paid Enterprise edition. Check the current feature split before assuming a specific capability is free, since where that line sits has moved over different releases. For a homelab or small-team deployment that just wants organized channels, threads, and search without federation or omnichannel ambitions, it’s the least operationally demanding of the three.

Mobile apps and day-to-day usability

This is where the gap between these three is bigger than feature checklists suggest. Mattermost and Rocket.Chat both ship mobile and desktop apps that behave like mainstream chat apps, notifications work reliably, and the UI won’t confuse anyone who’s used Slack or Teams before. Matrix’s Element app has improved a lot over the years but still has a reputation, deserved at times, for notification reliability issues and a UI that exposes more of the underlying protocol’s complexity (room versions, cross-signing verification, key backup) than a non-technical user wants to deal with. If the people using this chat server are not homelab enthusiasts themselves, that gap in polish is worth weighing heavily, because the best chat platform is the one people actually open instead of quietly going back to a group chat on their phone’s default app.

Resource footprint, roughly ordered

For a small deployment, Mattermost is the lightest of the three, a single binary and one database are easy to size and reason about even on a modest LXC. Rocket.Chat sits in the middle, the Node/MongoDB combination asks for more RAM than Mattermost at rest but is still comfortably runnable on typical homelab hardware for a small user count. Matrix via Synapse is the heaviest by a clear margin once you factor in federation and any public rooms you join, and is the one most likely to need a resource bump down the road if usage grows, which is the tradeoff you’re accepting for the federation and bridging capability the other two simply don’t offer.

Which one to actually run

If what you want is federation, bridges into Discord and Telegram and other networks, and end-to-end encryption as a default rather than an add-on, Matrix is the only one of the three that actually does that job, and Synapse (or Conduit if you’re willing to trade some polish for a lighter footprint) is worth the extra care in sizing. If you want a self-hosted Slack replacement for a small team or household and don’t care about talking to other servers, Mattermost gets you there with the least infrastructure to maintain. If you additionally want a customer-facing chat widget or omnichannel support routing bolted onto the same platform, Rocket.Chat is the one built for that combined job, accept the MongoDB dependency as the cost of that extra scope.

Bottom line

Don’t pick based on which one looks most like Slack in a screenshot. Pick based on whether you actually need federation (Matrix), the lightest possible Slack-shaped deployment (Mattermost), or chat plus customer-facing omnichannel features in one platform (Rocket.Chat). All three are mature, actively developed, and genuinely production-capable for a homelab. The failure mode isn’t picking unmaintained software, it’s picking the one with capabilities you’ll never use and then being surprised by the resource cost or operational complexity that capability was quietly asking you to pay for.