Currently, automated systems for program submission and assessment play a central role in the teaching of programming. A number of such systems have been developed in the last two decades. However, their adoption in regular programming teaching presents an obstacle: the overhead work required for the design of each problem, for compilation of problem collections, and for mundane management tasks. An open challenge is to make these systems easier to use and to reduce to a minimum the number of management tasks. In this article we present the FLOP system, which was developed to satisfy this goal. The contribution of the article is twofold. On the one hand, we present the FLOP system itself and its user-friendly features. On the other hand, we present in detail the user-centered design process used to design and enhance the ease of use of FLOP. Several actions were undertaken to inquire users’ concerns and needs, with a usability evaluation of FLOP conducted with students being the most fruitful action.