Personally (not wearing my Moderator Hat) I would say this is off-topic/not appropriate as a main site question, but it would be a good topic to discuss in chat.
At it's core this is a "List Of Things" question.
While not outright banned these are often a bad fit for Stack Exchange sites because they lead to a bunch of "Here's my favorite example" answers that are all equally valid, with none of them being definitively correct or objectively "better", so voting and accepting answers don't work the way they're intended to.
Answers to this sort of question also become obsolete quickly, particularly when we're talking about "open source operating systems", which tend to come and go as developers move on to other projects.
Stack Exchange Q&As do best with relatively static content (a question is asked and clearly answered) - they don't really lend themselves to active curation, which means in a year or two someone could come by, follow the links in the top-voted or accepted answer, and wind up at a dead link or abandoned github page. If we're lucky they'll tell us about it and someone will fix the link or revise the answer, but people will probably just become frustrated and the dead links / stale information will just reduce the overall quality of the site's content.