Dr. Geo is the GNOME interactive geometry software. It allows the creation of geometric figures and their interactive manipulation while respecting their geometric constraints. It was formerly called Dr Genius. A similar program, kig is part of the kdeedu package. The documentation is in a separate package, drgeo-doc, and it requires an html viewer such as konqueror (kdebase) or dillo to be usable.
WWW: http://www.ofset.org/drgeo/