I basically learned to program for Wheel of Time-based MUDs... first on The True Source, then on The Weave, and then on As the Wheel Weaves.

It was amazing how much drama existed behind the scenes and how there would be a family tree of staff/codebases stemming from that drama and stolen code/areas. As the Wheel Weaves is apparently not running anymore, but a few years ago I found a split of a split that still has an in-game game that I wrote that people still apparently play and enjoy. It's really gratifying.