Oleg Popov has recently started a new wiki called WiKi4All, which aims to be a catalog of wikis, where all existing wikis are listed in certain categories.
He's actively visiting loads of wikis and leaving a message for the maintainer to add his/her wiki to WiKi4All. I have already added Unmaintained Free Software there, and Crazy Hacks and Holsham Traders will follow soon.
Holsham Traders, by the way, is a realtime multiplayer trading game written in Ruby, which I'm currently developing (more on that later).