Feature Request: "Chat Rooms" or groups

I get asked for this a lot - Twitter doesn't do it.

• Rooms (or groups) that people can 'join'. When in a room, messages entered are only shown to the people in that room.

• Messages entered in the room have a hashtag appended (for later search)

• UI that allows user to easily enter a room, or to change rooms

• Admin permission function to assign who can enter a room

• Ability to search all the messages entered in a room (search by hashtag)