An extensive Minecraft server mod written for Bukkit. It is fairly old, originating from Sheograth's API, then transitioning into Bukkit, so it encompasses dozens of random features that I have added over time. In all, it has the functionality of probably about 5-10 separate mods, but is still not enough for most people to use independent of all other mods. Maybe eventually...
Large features:
-Complete multi-world support with a variety of world types
-IRC functionality
-PM system
Then lots...