Interesting niches you're interested in

I spend my free time doing math. Not serious math, mostly trying to figure out how to get simple graphing calculators to express complicated subjects.
(Examples of recent miniprojects: Electric field vectors, The Lamb-Oseen vortex, a particular solution of the Navier-Stokes equations of fluid motion, describing a simple vortex under the influence of viscosity, How flute tuning works)

Similarly, I also do a lot of recreational programming. Esoteric languages, simulation, and any math ideas that are too complex for graphing calculators. I was planning to write my own esoteric language at one point, but it got waylaid by Dwarf Fortress (which I play like two hours a day now, I should probably tone it down).