This blog forms part of the http://performanceGuru.com website which focuses on performance tuning UNIX-like Operating Systems (including Linux).
Version 3 of the famous Minix Operating system, has been released. The core kernel is under 4000 lines of code and it follows a micro kernel approach. There is also an updated version of the classic Tannenbaum book slated, to go with the code. Possibly a useful teaching aid and potentially a real-time O/S?