"ZenGen" is a script-tool which helps to automatically generate first-principles input files of all the ordered compounds of a given crystal structure in a given system. The complete set of heats of formation of each end-member can then easily be used in the thermodynamic phase modeling. "ZenGen" is a free and open source code, which can be downloaded from http://zengen.cnrs.fr. In order to illustrate its possibilities, the quaternary system, Cr-Mo-Ni-Re, has been investigated. The binary solid solution parameters have been estimated from SQS calculations. The σ−phase has been considered according to its crystal structure, i.e. with a 5-sublattice model, by the DFT calculation of the 4 5 = 1024 different ordered quaternary configurations. Several tentative ab initio phase diagrams are presented.