Tinix

Tinix, standing "Try It as miNIX-like operating system", is a tutorial operating system written by Yu Yuan. It is for teaching rather than using. In his book "writing OS DIY" (Publishing House of Electronics Industry, Beijing, 2006), Yu has given all the source of Tinix. 
Although Tinix borrows a lot of concepts and methods from Minix, it compensates for the practical programming skills, especially in x86 assembly, lacking from Tanenbaum's "Operating Systems Design and Implementation".