A collaborative mind map creation tool here
There's a big green button to create a mind map. Share the URL of the mind map with a friend and you should both see any changes the other person makes in real time.
Don't expect it to work too well I made it for fun and as an excuse to play with various technologies. But if you do want to tell me about a particularly annoying bug, ask for a feature try raising an issue and discovering that someone has actually found and used this might spur me on to fix it.