9front, seemingly Plan 9's de-facto successor, is almost surely quirky, often whimsical, at times nostalgic. It might even be functional, depending on how you define that[1]. Is actively developed, has a vibrant community. Puts an interesting spin on how you lay out systems, but doesn't diverge much from the Bell Labs formula. I'd certainly recommend giving it a shot, for the UNIX-inclined.
[1] I've daily driven it back in high-school, for all that's worth. Wrote assignments in troff and all. Some people might be able to tell of less mundane success stories as well.
I tried Plan9 as a minimalist desktop. I soon realised that three-button mouse chording isn't doable in this decade, and wish someone had written a Platinum-like window manager to replace rio.
[1] I've daily driven it back in high-school, for all that's worth. Wrote assignments in troff and all. Some people might be able to tell of less mundane success stories as well.