We report regularly about Visopsys - one of the few hobby operating systems that survived where virtually all the others (SkyOS, Syllable, etc.) died out. They've got a new website, which seems like a nice occasion to give it some attention again.
The bulk of Visopsys is a fully multitasking, 100% protected mode, virtual-memory, massively-monolithic-style kernel. Added to this is a bare-bones C library and a minimal suite of applications - together comprising a small but reasonably functional operating system which can operate natively in either graphical or text modes. Though it's been in continuous development for a number of years, realistically the target audience remains limited to operating system enthusiasts, students, and assorted other sensation seekers.