In case you're also interested in niche operating systems and are also disenthused by the fact that most of them are hot garbage, I will provide my list of interesting operating systems projects:
- 9front (<3)
* Caveat: heavily involve C++ for some fucking reason
@sir not temple/shrine OS? :P
I'm really interested in checking out 9front but I'm intimidated by plan9 and don't know where to start with it.
Fosstodon is an English speaking Mastodon instance that is open to anyone who is interested in technology; particularly free & open source software.