Effective tool support is much needed for the tedious and error-prone task of managing system requirements and system architectures. With the primary objective of providing practical support for software engineers, we have developed a tool for managing system requirements, system architectures and their traceability, which is being used in real-world industrial projects. The tool is based on a well considered information model of system requirements and architectures, and embodies a set of document templates providing guidance for software engineers. In this paper, we report on our experience in designing and improving the tool. In particular, we highlight a number of case studies that played a significant role in formulating the information model and document templates, and provide an assessment of the tool relative to existing practice.