http://www.geogebra.org/cms/
GeoGebra is a dynamic mathematics software for schools that joins geometry, algebra and calculus.
On the one hand, GeoGebra is an interactive 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.
GeoGebra has won a number of international awards.
Unfortunately, the language files seems to be creative commons non commercial which means you can’t sell this program and making it unsuitable for a commercial release of the OpenEducationDisc. 🙁
The language files are now Creative Commons Share Alike