AROS Research Operating System
AROS is an open source operating system that builds on AmigaOS. It can be run on powerpc and x86 hardware. It’s an independent, portable and free project, aiming at being compatible with AmigaOS 3.1 at the API level (like Wine, unlike UAE), while improving on it in many areas.
I don’t actually know that much about it, I just used it because I thought that it would be fun. As with ReactOS. Except that this one has an interesting logo.