The Many Faces of Polyhedrons - A Windows program in which you can interactively manipulate regular and semiregular polyhedra.
PEEK - A program to interactively explore arbitrary dimension polytopes through the use of cross-sections and projections.
POLY - Shareware Macintosh/Windows software for exploring and constructing polyhedra. Flattened versions (nets) of polyhedra may be printed and then cut out, folded, and taped, to produce three-dimensional models.
Polyhedra 2001 - OpenGL program which displays the uniform polyhedra and related shapes in real time. The shapes may be morphed in to their duals, exploded, truncated and unfolded into a net. Free download.
Polyhedra by Bob - Images and software. Poly is a free DOS program that can be used to study the truncations and transformations of the Platonic Solids.
PPL: The Parma Polyhedra Library - A C++ library for the manipulation of convex polyhedra. Distributed under the terms of the GNU General Public License.
Stella: Polyhedron Navigator - A program for creating, visualising, and printing nets for 3D polyhedra and 4D polytopes.