Unix: Minix3 ( A minimal Unix Clone )

Minix3
Website: http://www.minix3.org/
Download: http://www.minix3.org/download/

An introduction from the Minix 3 site:

"What Is MINIX 3?
MINIX 3 is a new open-source operating system designed to be highly reliable, flexible, and secure. It is loosely based somewhat on previous versions of MINIX, but is fundamentally different in many key ways. MINIX 1 and 2 were intended as teaching tools; MINIX 3 adds the new goal of being usable as a serious system on resource-limited and embedded computers and for applications requiring high reliability

This new OS is extremely small, with the part that runs in kernel mode under 6000 lines of executable code. The parts that run in user mode are divided into small modules, well insulated from one another. For example, each device driver runs as a separate user-mode process so a bug in a driver (by far the biggest source of bugs in any operating system), cannot bring down the entire OS. In fact, most of the time when a driver crashes it is automatically replaced without requiring any user intervention, without requiring rebooting, and without affecting running programs. These features, the tiny amount of kernel code, and other aspects greatly enhance system reliability."
~http://www.minix3.org/


Some of the greatest news to come to Minix 3 recently is that it was entered in Google's Summer of Code which will add mature code to jump start this minimal OS.

Url: http://wiki.minix3.org/en/SummerOfCode2010

Projects:
MINIX firewall
Multiboot compliance
Porting Pkgsrc
Unix domain sockets

I will have a couple follow-up segments in regards to Minix 3, but I encourage people to give it a shot. I understand its not for everyone though :)