Open-Source Massive Multiplayer Online Role-Playing Game engine. Server is semi-free, open for non-commercial use. Client is free software and the content is proprietary. Rehash from a 5-year-old project, active again since august 2007.
AgateLib - Awesome game and tool engine library. A platform independent .NET library for developing games and game development tools. AgateLib is built on a driver-based model so that new platforms and rendering pipelines can be implemented easily.