I'll start: I have a lot of deep appreciation for "changesets". It makes one of the hardest and most annoying parts of shipping NPM packages easy to wrap your head around.
zmk.dev, firmware for wireless mechanical keyboards that’s reliable and full-featured
Also it’s less niche but fish-shell. zsh gets lots of love but fish has all the best features included out-of-the-box
not sure whether it's niche, but few people know of jotai and it's an excellent piece of software
https://github.com/RonSijm/ButtFish Last year a professional chess player was accused of cheating. Due to the measures taken (metal detectors, etc) a chess streamer joked that he must've had a butt plug transmitting computer moves to him. This is the code for transmitting stockfish moves to a butt plug.
https://kindelia.org/ for computational-nerd interest and https://github.com/subconsciousnetwork/noosphere for knowledge-nerd interest