No, no other software from us is required in order to run ChemApp. Many customers also use FactSage for instance, because they prefer to have an interactive program available too, but there is no technical reason why FactSage is required (see also section 5.2).
Of course customers who also have FactSage (or ChemSage) benefit from the fact that they can create thermochemical data-files for ChemApp using FactSage and the databases they have available for these programs (see section 7.7).
While you don’t need any other software from us to work with ChemApp, you of course need thermochemical data (see section 7.1) and a suitable compiler (see section 4.1).