PALM is an advanced and modern meteorological model system for atmospheric and oceanic boundary-layer flows. It has been developed as a turbulence-resolving large-eddy simulation (LES) model that is especially designed for performing on massively parallel computer architectures including GPUs. Within our talk we give a short introduction to the model system PALM and give an overview on how we manage to develop and maintain the software. This includes a view on how we do source-code management, automated testing, and code documentation. We also give information on the many problems and difficulties which arise when working on an ever-growing software package with a team originally not based within the field of computer science.