Free package for quantum chemistry programming
Version: 1.6.3PyQuante is a free and open source suite of programs that will help you develop quantum chemistry methods. PyQuante is written in the Python programming language, but has many "rate-determining" modules also written in C for speed.
Operating System: Mac OS X
The resulting code, though not as fast as Jaguar, NWChem, Gaussian, or GAMESS, is much easier to understand and modify. The goal of this software is not necessarily to provide a working quantum chemistry program (although it will hopefully do that), but rather to provide a well-engineered set of tools so that scientists can construct their own quantum chemistry programs without going through the tedium of having to write every low-level routine.
NOTE: PyQuante is licensed and distributed under the terms of the BSD License.