Childsplay

Childsplay is a suite of educational games for young children, like gcompris, but without the overkill of c/c++ and the gnome environ. Also the use of the SDL libraries makes smooth animation and the playing of sound very easy. Childsplay uses a plugin system for the games, so you might want to check the Childsplay plugins page. (There are two built-in games: memory and a typing game.)

http://www.schoolsplay.org/

Claroline

Claroline is an Open Source eLearning and eWorking platform allowing teachers to build effective online courses and to manage learning and collaborative activities on the web. Translated into 35 languages, Claroline has a large worldwide users’ and developers’ community.

http://www.claroline.net

GCompris

GCompris is an educational software suite comprising of numerous activities for children aged 2 to 10. Some of the activities are game orientated, but nonetheless still educational. Currently GCompris offers in excess of 80 activities and more are being developed. GCompris is free software, that means that you can adapt it to your own needs, improve it and, most importantly, share it with children everywhere.

http://www.gcompris.net

GeoGebra

GeoGebra is a dynamic mathematics software for education in secondary schools that joins geometry, algebra and calculus.
On the one hand, GeoGebra is a dynamic geometry system. You can do constructions with points, vectors, segments, lines, conic sections as well as functions and change them dynamically afterwards.
On the other hand, equations and coordinates can be entered directly. Thus, GeoGebra has the ability to deal with variables for numbers, vectors and points, finds derivatives and integrals of functions and offers commands like Root or Extremum.
These two views are characteristic of GeoGebra: an expression in the algebra window corresponds to an object in the geometry window and vice versa.

http://www.geogebra.org/cms

jMemorize

jMemorize is a free open-source Java application that manages your learning processes by using flashcards and the famous Leitner system. jMemorize makes memorizing facts not only more efficient but also more fun. It boosts your whole learning experience and features categories, statistics and a visually appealing and intuitive interface.

http://www.jmemorize.org

Stellarium

Stellarium is a free open source planetarium for your computer. It shows a realistic sky in 3D, just like what you see with the naked eye, binoculars or a telescope.
It is being used in planetarium projectors. Just set your coordinates and go.

http://www.stellarium.org

Educative