TempleOS is a 64-bit, 2 megabyte, non-preemptive multi-tasking, multi-cored, public domain, open source, ring-0-only, single address space, non-networked, PC operating system for recreational programming.
Torrent included all Almanach about the system and its creator
There is good story about on several websites and videos example here https://www.youtube.com/watch?v=UCgoxQCf5Jg (https://www.youtube.com/watch?v=UCgoxQCf5Jg)