Chatrooms are way cool. You can restrict them, or open them to your default audience (I think this means anyone who can usually see your posts, in which case it depends on your channel permissions). They can last forever if you set 0min expiry (but can seriously slow the page down as they fill up over time), or they can expire by setting a time limit.
With a time limit, chats remain until you (everyone?) leave the room, and then everything older than the time limit goes poof.
You can have a look at mine if you like. Feel free to say stuff. Just don't say anything sensitive in the Eternal chat, because it'll be there forever (or until I delete the room). (Edit: I've deleted the Eternal chat, as it was laggy AF)
The best thing ever is the embiggen button in the top right of the chat. Hit that and it fills your screen and you can pretend there's nothing else in the world!