My main fields of interest are computer graphics and related topics. I have been using OpenGL since the day it was released in 1992. My experience spans both OpenGL drivers (from managing driver development at two leading companies, including hands-on feature, performance, and architecture work), and using OpenGL for scientific applications.
One interesting spare time project I worked on over the last few years (with long breaks) is a highly efficient and feature complete volume rendering library based on OpenGL: http://retokoradi.com/volume-rendering/.
Other areas of expertise include C++ and software architecture/design.