CodeCascades
Coding challenges arranged into cascades — series that get harder as you go, meant to sharpen your software engineering skills without feeling like homework.
Rails & Trains
A model railroading game for iPhone and iPad: build the track, then run the trains over it — puzzles to solve, or a freeform mode with no goal at all.
LifeSim
Conway's Game of Life for iPhone and iPad, on an infinite grid, with hundreds of known patterns built in.