In addition to Plan9 and the BSDs, which are Unixy and relatively familiar if you're coming from Linux/macOS, you could also checkout Haiku [0], which is quite

In addition to Plan9 and the BSDs, which are Unixy and relatively familiar if you're coming from Linux/macOS, you could also checkout Haiku [0], which is quite different and descends from BeOS. If you have an old TI calculator and want to try something other than a desktop OS, you could try out KnightOS[1]. As Shared404 mentioned, a Unix-inspired but quite new OS is Redox[2], which is written in Rust. Haven't used it at all, but it sounds like an interesting project. [0] https://www.haiku-os.org/ https://www.haiku-os.org/ [1] https://github.com/KnightOS/KnightOS https://github.com/KnightOS/KnightOS [2] https://github.com/redox-os/redox https://github.com/redox-os/redox