An alternative/custom Minecraft server, written in Java, compatible with the original protocol. OpenCraft is built upon Apache MINA, SLF4J, Jython and XStream. The aim is to have features not in the official server distribution, like antigrief/scripting.
This application is designed to facilitate the hosting of minecraft servers on a single computer and managing them remotely through a Java applet or jar interface.
UPDATE (19 Oct, 2012): As you can probably tell, this project is no longer maintained. If you wish to alter the sourcecode, feel free. If you would like to contribute to the project, email me at raenottingham at gmail dot com and I will add you as a contributor.