The Homepage of Sage:  www.sagemath.org

CompuTop for various computer tools for low-dimensional topology.

The Knot Atlas:  knotatlas.org

The Table of Knot invariants:  KnotInfo

The GecoGedi Project Homepage:  GecoGedi

An online version of Counter Examples in Tology: pi-Base

Lukas Lewark's homepage where one can find some computer programs for computing Khovanov-Rozansky homologies.