Minecraft Spoutcraft Servers

Spoutcraft is a framework to bridge the ever-widening chasm between single player mods, and multiplayer Bukkit plugins. Through it, Bukkit plugins can do the previously impossible. Currently, plugins can seamlessly manipulate and monitor inventory, audio, sound effects, skins, player titles, alter the main in-game HUD, and launch popup notifications on the player's client. http://dev.bukkit.org/server-mods/spout/