HaikuOS, simply FANTASTIC!
Out of curiosity are you using it as a daily driver?
I've tried early beta (2010 or so) and it was super fast but not enough to use it every day...
I installed Haiku on this Laptop from 1999 once since it was actually the only non-windows OS I could get to run for some reason. Video driver was bugged tho so the screen was visually offset by ~100 pixels which made it too hard to use. Otherwise though it ran at a bearable normal speed which is a huge feat for the something like 500MHz processor and 500MB/1GB of RAM (I forget the exact specs).