GEUP - Interactive Geometry software.
GEUP is an interactive geometry tool. Lets you dynamically explore Mathematics, build mathematical models of real world or create interactive mathematics presentations.
Great Math Programs
A collection of mathematical programs, with particular reference to geometry.
Math Forum: Search geometry-software-dynamic
Users of geometry software programs like Cabri Geometry II may share tips and advice at the geometry-software-dynamic discussion list.
Qhull for convex hulls, etc.
Qhull for computing the convex hull, Delaunay triangulation, Voronoi diagram, and halfspace intersection about a point.
Riemann surfaces visualisation
Unifpack is a set of programs and C libraries designed to help in the study of Riemann Surfaces.
Riemannian Geometry & Tensor Calculus @ Mathematica
Free Mathematica package for explicit tensor calculations in Riemannian Geometry.
UVModeller
A java applet that lets you input a surface function and view the surface interactively in real time.