OpenSourceStack (OSS) is a research initiative led by the Department of Advanced Powertrains at Chemnitz University of Technology (TU Chemnitz). The primary goal of the OpenSourceStack project is the development of proton exchange membrane (PEM) fuel cell and electrolyzer stacks for research and development purposes - completely free of confidentiality restrictions. The modular design allows for easy customization to meet specific research needs and experimental requirements. Currently, three standard cell sizes are available: OSS050: 50 cm² active area OSS100: 100 cm² active area OSS300: 300 cm² active area Additionally, a PEM electrolysis cell with a 50 cm² active area is currently under development and will soon be available. We also offer a comprehensive test system capable of supporting experiments up to 1 kW, enabling efficient performance evaluation and validation. For more information, visit our project homepage: mytuc.org/qhdp