A. Hawkins and N. Sinclair have written an article that has been published (online first) by International Journal of Computers for Mathematical Learning. The article is entitled “Explorations with Sketchpad in Topogeometry“, and the authors describe how they created several microworlds of topological surfaces using The Geometer’s Sketchpad. Among the surfaces described are: the Moebius strip, the torus and the Klein bottle. The article contain lots of interesting examples and information about topological geometry, as well as about using this particular software.
(See also this list of interactive geometry software!)