The 64 Bit Temple Operating System is a Games & Entertainment::Tools & Editors software developed by Temple Operating System. After our trial and test, the software was found to be official, secure and free. Here is the official description for The 64 Bit Temple Operating System: 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. you can download The 64 Bit Temple Operating System 4.07 free now.