hi,
both FE software are GPL and should not against each others. CalculiX CGX has a feature to export element and node sets in Code_Aster format, also UNV mesh and node groups generated by Salome preprocessor (modeling & meshing) dedicated specially for Code_Aster can be exported to CalculiX input files.
User has possibilities’ to switch between of both FE solver if required to further study the area of interested (e.g analysis type, material laws, element formulations).
best,