McMMO is an open source plugin for the Minecraft multiplayer server mod for http://www.spigotmc.org/resources/mcmmo.2445/ and Bukkit(Note Bukkit no longer supports new verisons of the McMMO plugin) that is currently under development by . This plugin allows for an RPG-like experience to exist in the world of Minecraft complete with pointers, normal powers, dog food parties, PvP (Player vs Player) and more!
New versions are being released frequently, so be sure to check the links and stay up to date!
You can discuss McMMO and submit suggestions/feedback at the Bukkit thread.
McMMO Player Content
McMMO's main function is to incorporate an RPG-like skill system that players will have access to right from the beginning. Depending on how much a certain tool is used or a certain action is performed, players will gain experience that will eventually add bonuses such as double drops, rare drops, or ability enhancement.