The
KnotPlot Site 
Robert Scharein's Knot Manipulator and
Visualizer 
JavaView 
Geometry and Visualization Software by Konrad
Polthier, Eike Preuž, Klaus Hildebrandt and Ulrich Reitebuch. 
jDvi 
Java based DVI viewer by Tim Hoffmann. 
Polymake 
Algorithmic treatment of polytopes and
polyhedra by Michael Joswig and Ewgenij Gawrilow 
Surface
Evolver 
Ken Brakke's Surface Evolver for Variational
Problems 
Cinderella 
Geometry Software by Ulrich Kortenkamp and
J’rgen RichterGebert. 
Kant 
Computer algebra system for algebraic number fields by Michael E. Pohst 


MathNet
Software 
Mathematical Software Archive at MathNet. 
Mathematics
Virtual Library 
Listing of Mathematics Software at Florida
State University. 