OOSMOS, the Object Oriented State Machine Operating System, is an open source implementation of threadless concurrency for C/C++. The portable, single-source file implementation makes it easy to integrate into any environment - from bare boards to mainframes. Out of the box, it compiles and runs on many small processors and boards (including Arduino) as well as on Windows and Linux. It is our goal for developers of any skill level to be able to use OOSMOS effectively, whether building a science project on an Arduino or building an advanced medical device.
We've already talked about OOSMOS before, but the project's just gone open source.