Litnerd - The Pixar for education, reading program for K-5 schools
MathIsFun Times Table - Learn Your Multiplication Tables
Cotrio - The most beautiful way to move your brain and imagination
GCompris - Educational Game for Children 2 to 10 years old.
WonderBox - Wikipedia for kids — Learn with friends and family
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.