This is a simple python script that wraps around the official minecraft.net server. It implements a plugin system based on the parsing of log output. It also includes a remote control available via TCP, in addition to automatically updating the server when updates are released.
The newest addition to OpenCraft is NBT-Edit, a named binary tag editor. Here you can see it editing a player's inventory in Minecraft Alpha. It is very much a work in progress, but the source is available at http://gitorious.org/opencraft/nbt-edit for the brave ones.