MOLGEN
Program for the automatic generation of constitutional isomers and combinatorial libraries, for Unix/Linux and WinNT/95. Free demo available.

Molecule for Macintosh
Structure editor. Especially suited for computational chemistry, supports several file formats and operations such as animations and optimizations. License fee required.

Mol2Mol
Molecule file manipulation and conversion shareware for Windows. Works with about 40 file formats. Screenshots, downloads, and purchasing information.

Marvin
Java applets for the web developer who builds chemical internet/intranet sites. The package contains an applet for editing and visualizing molecules on a web page and one for viewing molecules on a web page.