GPS (Genesis Population Synthesis) develops population synthesis models. The code suite uses the Genesis database of planet formation models for small exoplanets (super-Earths and Mini-Neptunes). Although the codebase focuses on the Genesis models, aother models can easily be integrated with GPS. It computes the bulk compositions of the planets and simulates atmospheric loss and evolution to find the final states of the planets that can be observationally verified. GPS also offers tools to process and analyze the data from recent observations of small exoplanets in order to compare them with the models.