I make the specification of non-linux because otherwise this would just become a thread full of obscure distros that do the same thing as a million other distros.
Some lesser known OSs:
- AROS - based on Amiga OS, has some derivatives like IcarOS and MorphOS
- Haiku - based on BeOS
- Redox - Unix-like, made in Rust (might technically count as linux?)
- Serenity - Unix-like, very late 90s look and feel
- Kolibri - Tiny OS, the image is ~44MB. It also has a smaller version that fits in a single floppy.
- PhantomOS - When 3 Russians decide to turn everything about a typical OS upside down.
To name something that hasn’t been mentioned yet, ArcaOS, which based on OS/2. It supports modern hardware and in addition to some preinstalled software, it also has some compatibility layers to run software from other OSs.
I still remember the huge marketing push IBM put into it in the mid-90s. Who would have thought it wouldn’t take off when they never actually showed what it looked like. Just a bunch of people describing it.
https://m.youtube.com/watch?v=5dtlwInFhlk