PyQuante is an open-source suite of programs for developing quantum chemistry methods. The program is written in the Python programming language, but has many "rate-determining" modules also written in C for speed.
NWChem is an electronic structure package that features MC-SCF, MPn, CC, CI, and DFT methods. Properties, solvation models, QM/MM, and MD simulations are also possible.
C. Wild, K. Maly, C. Zhang, C. Roberts, D. Rosca, and T. Taylor. TENCON '94. IEEE Region 10's Ninth Annual International Conference. Theme: Frontiers of Computer Technology. Proceedings of 1994, (August 1994)