I finally decided to release the code for HeadCloud, the software I used to run ThinkBot, as I haven't the time or the server to keep it running and gather enough users. Also, a couple of people had expressed interest in using the idea in their own projects.
HeadCloud is a Napster-style service, where people connect to a central hub, send a list of the thoughts they want to share, and search the database of other people's thoughts to see who they want to connect to. It's called HeadCloud after the original vision - being able to walk down the street and see little clouds above people's heads that showed what they were thinking.
Anyone can run their own, specialist hub (based around a particular geographic location, for example). The only requirements are Perl, MySQL and Net::Jabber (which has a few small XML-parsing requirements of its own), and a server that doesn't shut down scripts at regular intervals.
You can download HeadCloud here. Make sure I get credit for the original code, and please let me know if you make any useful additions or alterations.