Software applications dependent on frequent user interaction need user interfaces with a high degree of usability. However, creating high usability user interfaces is a challenging task for software developers. The results may be highly dependent on individual developers‟ knowledge about usability. User-Centered Design suggests another approach, possibly giving more predictable results: to involve users in the development and evaluation of the user interfaces. To enable such user involvement, we developed a web application called the Design Feedback Tool. It presents multiple design alternatives to users and allows them to comment and rate them. A tailored development method was used for creating the specification, design and implementation of the application. Furthermore, a paper prototype of its user interface was evaluated using the Heuristic Evaluation method, and a security risk analysis was conducted. Documentation and lessons learned may be useful for software developers and researchers creating similar applications, as well as for research into use of software development methods. Furthermore, the results of the prototype evaluation and security risk analysis may be of interest to researchers in these areas.