Jenn 3d is a program for visualizing Coxeter polytopes. It was created by Fritz Obermeyer and it is released under the free GPLv2 license.
Jenn is a toy for playing with various quotients of Cayley graphs of finite Coxeter groups on four generators. Jenn builds the graphs using the Todd-Coxeter algorithm, embeds them into the 3-sphere, and stereographically projects them onto euclidean 3-space. (The models really live in the hypersphere so they looked curved in our flat space.) Jenn has some basic motion models governing the six degrees of freedom of rotation of the hypersphere.