Yes, TNet comes with a pre-compiled server you can launch anywhere. It's about 50kb, and is mono-based, so will run on Windows, OSX and Linux.
You can launch that executable as a lobby server or as a game server (and of course you can do the same thing from within Unity without having to launch anything).
Just note that a lobby server is for servers -- servers register with it, and you can retrieve a list of these servers. It's not a place to chat. If you want a chat room, you need to join an actual game server and either join a channel or use broadcasts.
Each channel can be a separate multiplayer game instance.