As a result of Hey0 quitting the hMod project, a new server mod project has surfaced. Bukkit, an open source server mod was announced yesterday, January 1st by EvilSeph on the Hey0 forums. Hundreds of users have since flocked to the Bukkit forums at http://www.bukkit.org.
Bukkit has been categorized as a community project, and dozens of plugin developers have already started playing around with the source, including me. The official Bukkit dev team consists of 9 developers, but anyone can create their own Bukkit plugins. One unique thing about Bukkit is that they have their own Plugin Repository, so you can always find as many plugins as you need in one place. The plugin repository is located at http://fill.bukkit.org/ (Fill the Bukkit, get it?)
The Bukkit project is still fairly new, so there aren't many updates to report on. I'll be updating you once more updates come out. One thing's for sure, this mod will be sweeping across hundred of Minecraft servers before we know it.