Slack's Free plan hides every message and file older than 90 days, so last quarter's incident thread or deploy postmortem disappears from search until the workspace moves to Pro. Pro bills per active member, and SAML SSO and data exports only arrive on Business+. Zulip, Mattermost, Rocket.Chat, Element's Synapse, and Tuwunel keep the full message history in a database you operate (PostgreSQL for Zulip, Mattermost, and Synapse, MongoDB for Rocket.Chat), so retention depends on your disk and your own policy instead of a plan tier. The two Matrix homeservers, Synapse and Tuwunel, add federation between independent servers and can be deployed from a Docker image or a single Rust binary.
| Name | Main Category | Sub-Category | Target Alternative | Free Tier Summary | Self-Hostable? | Short Description | Primary Link |
|---|---|---|---|---|---|---|---|
Tuwunel | Project Management & Developer Workspaces | Lightweight Matrix Homeserver | Slack | 100% Free - Self-Hosted (Apache 2.0) | Yes - Binary | Rust Matrix homeserver that ships as one small binary or a Docker image, and works with existing Matrix clients, bridges, and bots. Fits small teams that want Matrix federation without running Synapse. | |
Element (Synapse) | Project Management & Developer Workspaces | Federated Matrix Chat | Slack / Microsoft Teams | Free - Self-Hosted (Synapse is AGPL-3.0). Element Server Suite Community is the free official distribution for small-to-mid-scale, non-commercial use; commercial licenses are sold separately. | Yes - Docker | Matrix homeserver with end-to-end encrypted rooms and federation across independent servers, used with the Element web and mobile clients. Supports workers and PostgreSQL for larger deployments. | |
Zulip | Project Management & Developer Workspaces | Topic-Threaded Team Chat & Collaboration | Slack / Microsoft Teams / Basecamp | 100% Free - Self-Hosted (Apache 2.0). Mobile push is free for up to 10 users; larger orgs need a free Community or paid plan for the push relay. | Yes - Docker | Topic-threaded team chat running on PostgreSQL with full-text search, REST API, and built-in integrations. Organizes discussions into streams and named topics, serving as a self-hosted, unmetered alternative to Slack's history limits and Basecamp's messaging suite. | |
Rocket.Chat | Project Management & Developer Workspaces | Team Chat & Omnichannel Messaging | Slack Pro / Business+ | Free - Self-Hosted (MIT-licensed Community core; free Starter plan capped at 50 users). Mobile push notifications relay through the Rocket.Chat Cloud gateway. | Yes - Docker | Channels, threads, video calls, and an apps engine for bots and integrations, backed by MongoDB. Also handles customer-facing live chat from the same server. | |
Mattermost Team Edition | Project Management & Developer Workspaces | Self-Hosted Team Messaging | Slack Pro / Business+ | Free - Self-Hosted (MIT Team Edition: no message cap, up to 250 activated users, no SSO). The v11 Entry edition caps visible history at 10,000 messages. | Yes - Docker | Slack-style channels, threads, and slash commands on a Go and PostgreSQL stack, with webhooks and a plugin framework for DevOps workflows. Install the Team Edition build to avoid the Entry message-history limit. |
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