Mattermost
Team Chat
Self-hosted team chat with channels, calls, playbooks and boards, as a free MIT build or a commercial subscription.
Also offers paid editions — see the detail.

Self-hosted means you run the software on infrastructure you control. Some of it is free, some of it is paid — both belong here, and every entry states which one it is.
Every entry shows the price model and the licence of its self-hosted edition.
Team Chat
Self-hosted team chat with channels, calls, playbooks and boards, as a free MIT build or a commercial subscription.
Also offers paid editions — see the detail.
Team Chat
Self-hosted team chat with messaging, voice and video; free Starter and MIT Community editions, paid plans by quote.
Also offers paid editions — see the detail.
Team Chat
Open-source team chat with topic-based threading, self-hosted on your own Ubuntu or Debian server.
Also offers paid editions — see the detail.
Free and paid, clearly splitEvery entry states the price model of its self-hosted edition. A paid cloud plan never implies the self-hosted edition is paid.
Licence is not priceOpen source, source-available and proprietary are separate facts from what an edition costs, and both are shown.
Unknown stays unknownIf we could not read a price from a vendor source, the entry says so instead of showing a guess.