PixelWhimsy - a software toy for toddlers and young children. But in truth, people of any age like playing with it. I wrote it especially for tots as an alternative to the candied package software that is marketed to kids.
MathFactz - Create worksheets to practice arithmetic
(Formerly Eittris) - Multiplayer Tetris with powerups.
Dot Game Studio - Print up pages of the dot game that are mostly filled in.