CRACK: Educational Software to Practice Calculating: Provides arithmetic tasks to be solved on Windows. These tasks begin very simple and get harder.
EURO Game: Learn about the new European currency. (Windows)
GCompris: [Unix] Distributed under the GPL. For young children, includes activities like discovering the mouse and keyboard, telling time, puzzles, memory games, and reading training.
Gear-Up: Create virtual flash cards for DOS from study material, test yourself, and keep score.
Jaw Wars: Brush those teeth and defeat the germs before they rot and drop out. One player, simple click Shockwave game.
Maths Race: Give the right answer to every questions to win the race. (Windows)
Picture Perfect: Test your observation ability on Windows by finding the differences between to photographs.
Tux Typing: Typing tutor for Linux, BeOS, or Windows starring Tux the penguin. [Open Source, GPL]