AmigaOS is described as 'The proprietary native operating system of the Amiga and AmigaOne personal computers, introduced with the launch of the first Amiga, the Amiga 1000, in 1985' and is a operating system in the os & utilities category. There are more than 100 alternatives to AmigaOS for a variety of platforms, including Linux, Self-Hosted, BSD, Windows and Mac apps. The best AmigaOS alternative is Linux Mint, which is both free and Open Source. Other great apps like AmigaOS are Ubuntu, Debian, Fedora and Arch Linux.
This is the open source, spiritual successor to Amiga and BeOS. The 32 bit version can run BeOS programs. Note that it's still in beta and unlikely to even boot on virtual machines.