Tor allows clients and servers to offer hidden services. That is, you can offer a web server, SSH server, etc., without revealing your IP to its users. In fact, because you don't use any public address, you can run a hidden service from behind your firewall.

Neat! The Tor people have implemented an eternity service, and there is a Wiki in it with a site directory! I finally have a reason to bother with Tor, if for no other reason then to have a look at this anonymous community.