Bukkit

Capture and convert mobs to spawn eggs with their attributes preserved.

Displays horse stats such as jump height, speed, health, etc. with additional commands.

Tether adjacent pressure plates together for simpler redstone circuits

Multiple parties with GUI controls and shared inventories

Allows you to /sudo players with YOUR permissions instead of theirs

Allows you to recolor glass and hardened clay in the world as well as scrape off the dye.

A plugin that allows people to turn into a fern.