Jmol
Jmol is an open-source Java viewer for chemical structures in 3D with features for chemicals, crystals, materials and biomolecules. For example one can view xyz files etc.
How to obtain Jmol
Jmol is free to download. Visit the Jmol website for full instructions.
How to run Jmol
Jmol can be used as a stand-alone program, and as such can be launched using the command:
java -jar Jmol.jar