The FOX program was made for the ab initio crystal structure solution from diffraction data (mostly powder diffraction data). Its most interesting features for ab initio structure determination are:
* a versatile description of the crystal contents: either isolated atoms, molecules described using a bond length, bond angles and dihedral angles, and polyhedra for inorganic compounds. You can describe your structure by using any combination of groups of atoms, using a chemist's or crystallographer knowledge about the connectivity in your sample to constrain possible solutions;
* an automatic correction for special positions and shared atoms between polyhedra, suitable for global optimization algorithms;
* the ability to use simultaneously multiple powder patterns (X-rays, neutrons), as well as single crystal data (e.g. extracted from a powder pattern);
* smart global optimization algorithms which can get out of false minima;
* a graphical interface with a 3D crystal structure view, with live updates during the optimization process.

This program can be used also for educational purposes, to show a 3D display of Crystal structures, and the associated powder pattern(s) (see how adding atoms, changing the lattice, or changing the spacegroup affects the powder pattern and the 3D structure).

Reference:
J. Appl. Cryst. 35 (2002), 734-743, V. Favre-Nicolin and R. Cerny, FOX, 'free objects for crystallography': a modular approach to ab initio structure determination from powder diffraction