9front is one of the most fascinating pieces of software that I know of. The devs are in this strange retrofutristic, idealist bubble where they are making their ideal OS, and don't care about the outside world (for it is tainted by unclean programming paradigms). Fun to watch, nonetheless.
This probably makes 9front the only OS still in development to have manuals in book format. Who else misses those old microsoft documentation that used to ship with their software in the 90's and before? I was never a fan of their company, but that aspect of their software in particular was awesome.