I have been a long time user of Linux system (Fedora, RedHat, CentOS, Debian and Ubuntu). I have also worked on Windows and Mac.
While programming I realized that every new programming language I learnt introduced me to new ways of doing things that I think has helped me mature as a programmer.
I am looking for a similar experience with operating systems. What operating do you suggest that would help me to explore something new and interesting?
A couple of constraints:
* Should not be another Linux distribution
* Should not be too esoteric or obscure operating system. I know this is subjective. If this filters out all operating systems you might have suggested, then please suggest the least esoteric or the least obscure one.
* Good documentation or clean source code is a plus because it would help me to study and learn it more effectively