I really enjoy low level development... things like OS and compiler design. Emulation, simulation, etc. It's sad there's very little place for these "hobbies" anymore, other than that, a hobby.
You can contribute to open source compilers. It’s both fun and beneficial.
And just like child rearing and homemaking, another line of work fundamental to the well being of society goes unrecognized, underpaid and expected to be done out of love while other profit from it.