The Usability Engineering Repository (UsER) is a flexible development environment to support collaborative analysis, design and evaluation of interactive human-machine systems. For this purpose, UsER provides several modules, which cover different aspects and methods of the development of human-machine interfaces. UsER supports the contextualized development of user interfaces in a broad range of application areas like office systems as well as safety-critical control systems by providing general as well as domain specific analysis, design and evaluation modules. These modules may be applied as needed and their contents will be cross-referenced through linked entities and hypermedia relationships. This semantic network created through analysis, design and evaluation can be mapped into linear document structures for formal development purposes, especially for project deliverables and contracts. UsER can be integrated with other development environments through a standardized requirements interface as well as a standardized process model interface.