Software

TTC - Mathematica package for doing tensor and exterior calculus on differentiable manifolds.
http://baldufa.upc.edu/xjaen/ttc/

Singular - Computer algebra system for polynomial computations. Free download.
http://www.singular.uni-kl.de/

Geometria - A Java program in solid geometry. Solids can be measured, cut, drawn upon. 60 sample problems with resolutions.
http://geocentral.net/geometria

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.
http://www.geup.net

GEUP - An interactive geometry program for Windows. Evaluation version free to download.
http://www.geup.net/index_eng.htm

Symmeter - An on-line tool for understanding and measuring symmetry.
http://www.symmeter.com/

KSEG Interactive Geometry Software - KSEG is an Open Source program for interactively exploring geometric constructions which can be used to teach geometry in the classroom or for personal enjoyment.
http://www.mit.edu/~ibaran/kseg.html

C.a.R. Geometry Program - A free program allowing Compass and Ruler constructions. Now also available in Java.
http://mathsrv.ku-eichstaett.de/MGF/homes/grothmann/car.html

Home Page of Isard - A free dynamic geometry package for Windows, PowerMac and Linux. Like Cabri, but in Smalltalk (and smaller). Source available : you can extend it as needed !
http://www.jeannot.org/~js/isard/

Lissajous Figures by Geo Doubek - Applet that draws the famous Lissajous Figures, with mathematical explanations about it, by Geo Doubek.
http://www.angelfire.com/falcon/geodoubek/

GANG Software Suite - A set of mathematical environments for computing, visualizing and experimenting with geometric objects; built with the OpenGL/Mesa library and the GTK+ user interface.
http://www.gang.umass.edu/software/

Ricci - A Mathematica package for doing tensor calculations in differential geometry.
http://www.math.washington.edu/~lee/Ricci/

MowMowMow's Cabri Room - Many Cabri files aimed at high school level geometry.
http://www.mowmowmow.com/math/cabri/index_e.htm

Rite Item - Geometrical shareware software. Anyangle (Windows/DOS) finds answers to problems involving triangles. Partydot creates patterns.
http://www.riteitem.com/

WinGCLC - a tool for describing geometric constructions and making digital illustrations in LaTeX and bitmap format.
http://www.matf.bg.ac.yu/~janicic/gclc/

Riemannian Geometry & Tensor Calculus @ Mathematica - Free Mathematica package for explicit tensor calculations in Riemannian Geometry.
http://www.inp.demokritos.gr/~sbonano/RGTC/

Dr. Geo - An interactive geometry program for Linux, distributed under the GNU public license. (Free)
http://www.ofset.org/drgeo

Qhull for convex hulls, etc. - Qhull for computing the convex hull, Delaunay triangulation, Voronoi diagram, and halfspace intersection about a point.
http://www.qhull.org

KwikTrig - A free trigonometry solving program for Windows.
http://www.fracaro.net/kwiktrig.htm

The Geometer's Sketchpad Resource Center - This Resource Center supports users of The Geometer's Sketchpad "Dynamic Geometry" software. Contents include a freely-downloadable demo and Java versions; research bibliography; online activity guide; technical support center.
http://www.keypress.com/sketchpad

Riemann surfaces visualisation - Unifpack is a set of programs and C libraries designed to help in the study of Riemann Surfaces.
http://www.geom.uiuc.edu/apps/unifweb/about.html

Cinderella: Interactive Geometry - Cinderella is a Java based interactive geometry tool. The only available tool that gives correct solutions to typical geometrical problems.
http://www.cinderella.de/

Polyhedron - Interactive application for solid geometry with 250 built-in problems. Simulates ruler, compass, protractor and other tools. Solids can be cut, displayed differently, rotated, joined again.
http://www.geocentral.net/polyhedron

UVModeller - A java applet that lets you input a surface function and view the surface interactively in real time.
http://www.geocities.com/hirak_99/java/uvmodeller.html

Cabri Geometry - The home site for Cabri Geometry, a dynamic geometry package .
http://www-cabri.imag.fr/index-e.html

Great Math Programs - A collection of mathematical programs, with particular reference to geometry.
http://www.xahlee.org/PageTwo_dir/MathPrograms_dir/mathPrograms.html

Cabri Java beta version - Create dynamic geometrical figures using Cabri and publish them as Java applets.
http://www.cabri.net/cabrijava/