I Know It - "I Know It" is an online game for practicing primary-level math concepts.
HoDoKu - HoDoKu is a sudoku helper written in Java and available in English and German.
GCompris - Educational Game for Children 2 to 10 years old.
Yasminoku - Sudoku game and solver totally written in DHTML.
childsplay - Childsplay is a collection of educational activities for young children and runs on Windows, OSX, and Linux. Childsplay can be used at home, kindergartens and pre-schools.
USB Sudoku - A very small program for playing the original game of Sudoku.