MOPAC (Molecular Orbital PACkage) is a general-purpose semiempirical quantum mechanics package for the study of chemical properties and reactions in gas, solution, or solid-state (see Wikipedia article about the MOPAC).
In 2007 James Stewart released MOPAC2007 (an improved version of MOPAC 7.1), which is free for academics. On-line manual is here
There are also commercial versions of Mopac sold by (among others) Fujitsu for Versions 2000 on up
Send all questions, suggestions and comments to Vlad (email@example.com)
Dr. Vladislav Vasilyev
The Australian National University,
Canberra, ACT, 0200, Australia