Avogadro - Avogadro is a free, fantastically easy to use molecule editor.
ImageJ - and Other Health Care
Jmol - Jmol is a free, open source molecule viewer for students, educators, and researchers in chemistry...
pymol - PyMOL is a powerful and comprehensive molecular visualization product for rendering and animating...
ACD/ChemSketch - ACD/ChemSketch for personal and academic use brings the power of our structure drawing package to your home computer.
Virtualmin - It includes numerous features not in the GPL version (like script installers, resellers, HTML editor, an improved UI, mobile access, spam and virus filtering).