Program Description
TempleOS is a free, public domain, open source, x86_64, non-preemptive multi-tasking, multi-cored, ring-0-only, single-address-map (identity-mapped), non-networked, PC operating system. Paging is, basically, not used.
Includes 64-bit compiler, assembler, unassembler, boot loaders, games, utilities and tools, graphics library, support for VGA, keyboard, mouse, CD/DVD, hard drives.
You will probably run it in VMware, VirtualBox or QEMU, however, it does work natively on some 64-bit machines from 2004-2011.