I always forget about Bonjour. It's one of those neat little Apple technologies that would really make the world a better place if more systems supported it.
What is it?
In a nutshell, Bonjour lets your computer see all available services on all other computers in your local network. This information doesn't go out on the internet (although there is a thing called Wide Area Bonjour which I haven't looked into much yet).
Example of Bonjour + Apache more...