Geometry Expressions

Geometry Expressions is the world's first Interactive Symbolic Geometry System. This means: Geometric figures can be defined by either Symbolic Constraints or numeric locations. Measurements on your drawing are not only presented numerically, but also expressed symbolically as Mathematical Expressions. Your drawing comes to life via parametric, symbolic animation. All the usual constructions are available but also powerful, new symbolic constraints. Geometry Expressions can be used as a stand-alone program or in conjunction with your favorite algebra system via MathML input and output. Think of Geometry Expressions as a geometry front end for your algebra system. Or think of it as an algebraic extension of your geometry system. Or think of it as a stand alone system that puts the mathematics back in geometry.

http://www.geometryexpressions.com