A wiki is an on-line encyclopedia that can be modified and added to by users. It usually includes simple methods to link articles without resorting to HTML. One of the largest examples is Wikipedia, but there many others dedicated to different subjects, such as software projects.

My friend Simon has recently created his own wiki based around interesting engineering and architecture around the world. My own, minor, contribution was a piece on the new Wembley Stadium.

I'm pleased to see the wiki includes some nice semantic data for things like location and links.