PyPSA is a Python-based open-source toolbox for energy planners. It enables cost-efficient, flexible, transparent and trusted investment and operational planning of modern energy infrastructure on a local and continental scale. With over 1000+ GitHub stars, it is the most popular toolbox for network operators, utilities and policymakers. Our nonprofit, Open Energy Transition (OET), is the leading commercial support arm of PyPSA with several paying customers. By improving open-source software and open data and by providing consultancy services, massive open online courses, and global applicable open decision-support software platforms, OET aims to accelerate the energy transition worldwide. Users of the software include the European Commission, Canadian Energy Regulator, Stanford University, Shell, Tata Steel and TransnetBW.