Embedded Operating System
ADEOS (A Decent Embedded OS) is a very simple OS written in C++ mostly (around 1000 lines of source code) and explains the basic needs of an embedded Operating System.
I read about this in the book "Programming Embedded Systems in C and C++" by Michael Barr. This could be used for people who are interested in writing RTOSes or improving upon them. Moreover, the book gives good info about programming in C/C++ for an embedded system, main concerns in processor, peripherals, Memory & OS.
You can FTP the source from
ftp://ftp.oreilly.com/examples/nutshell/embedded_c
More on the book and examples at this site
http://www.netrino.com/Books/EmbeddedC/examples.html