Hypercube Downloads by Rudy Rucker and Farideh Dormishian: A shareware program for Windows called Hypercube 98 that shows tumbling four-dimensional hypercubes as well as some 3D polyhedra and some 2d snowflakes.
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 polyhedra.
The Many Faces of Polyhedrons: A Windows program in which you can interactively manipulate regular and semiregular polyhedra.