GeoGebra is a dynamic mathematics software that joins geometry,
algebra and calculus. It is developed for education in secondary
schools by Markus Hohenwarter at the University of Salzburg.

You can do constructions with points, vectors, segments, lines,
conic sections as well as functions and change them dynamically
afterwards. 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.

GeoGebra received several international awards including the European
and German educational software award.

WWW: http://www.geogebra.org/