Dudeball NG is an arcade game for one or two players. The rules are simple: each player has to take 'the dude' to the opposite side of the playing area.
Henry's Spaceship Shooter is a tiny arcade game for one player. It is based on libSDL, libSDL_ttf, and libSDL_image. The graphics are black-and-white, which makes the files very small.
A Linux-based network gateway.
A library that efficiently calculates various mathematical functions using SSE2 SIMD instructions in double precision.