GenX is a scientific program to refine x-ray refelcetivity, neutron reflectivity and surface x-ray diffraction data using the differential evolution algorithm. GenX is very modular and highly extensible and can be used as a general fitting program.
An intuitive molecular editor and visualization tool
Avogadro is an advanced molecular editor designed for cross-platform use in computational chemistry, molecular modeling, bioinformatics, materials science and related areas. It offers a flexible rendering framework and a powerful plugin architecture.
--UPDATE-- New Version is now integrated in the official PyMOL plugin repository! --UPDATE--
The BNI (Beyond Normal Interaction)- Tools is a plug in for the PyMOL molecular visualization system which adds additional functionalities and presets to the PyMOL GUI and also adds useful extended commands.