GDIS - a GTK based program for the display and manipulation of isolated molecules and periodic systems.
GDPC - a program for visualising molecular dynamic simulations, it is a very versatile program and could easily be used for other purposes.
DX - Open Visualization Data Explorer is a visualization framework that gives users the ability to apply advanced visualization and analysis techniques to their data.
Crystal Studio - a Windows 9x/NT/2000/ME/XP software package for crystallography.
Ortep - a program for drawing crystal structure illustrations.