They're for playing puzzley games in real time.
Each of them has a pinned message to explain the rules of the game. Anyone is welcome to take part, and the room owners tend to be people who are particularly active players of the game (or, sometimes, bots whose automatic pinning powers are necessary for playing the game).
Contact
Codenames
Spyfall
Zendo
Detailed rules here on this meta thread - NEEDS MAKING!
Strupremum
Detailed rules here on this meta thread - NEEDS MAKING!