Ignis has a mod called Carbon that's a personal favorite of mine. It's a super lightweight material mod that used to serve as a chemfuel sink in the days of old. Not necessarily a problem in current versions of the game, but it still enjoy having mid and end game building materials that I can work towards.

Hades's Rimworld Farming is also a solid under the radar pick for me. I like the idea of being able to improve the quality of soil, but I kind of hate the overhead of trying to till each tile before your workers can plant anything, so this strikes a nice compromise. I've never felt that it was too crazily overpowered, since growing/ hunting foodstuffs, processing it, and then fertilizing the ground can be pretty resource/labor intensive. Plus, because it's a floor it prevents trees from popping up and blocking your turbines.

sch518's Vaccines is a really nice and elegant way to fend off plagues and illnesses without having to start up a drug empire to mass produce Penoxycyline.

DaLLaN's Cyber Fauna deserves an honorable mention. It's on the bigger/ more popular side, but still where near the extent that a dog said is. Which is a shame, because I've found Cyber Fauna to be way more broadly compatible and generally less cluttered. One of favorite runs involved taming a Gallatross from Alpha Animals (via inspired taming), and then promptly turning it into a bionic marshmallow of death and destruction.