Swarm robotics in real world requires a large number of robots and thus enough room for experimentation. Therefore, to implement such experiments with limited budget, robots should be compact and low cost, which entails the use of microcontroller-based miniature robots. In this context, developing behaviour is challenging, because microcontrollers are not powerful enough to support common high-level development environments such as Java. Furthermore, the development tools for microcontrollers are not able to monitor and debug groups of robots online. In this paper, we present a new event-based control architecture: ASEBA. It solves the problem of developing and testing collective behaviours by running script inside a lightweight virtual machine on each microcontroller and by providing an integrated development environment to program and monitor the whole group of robots from a single application running on any desktop computer. We have validated ASEBA by implementing a dangerous-area avoidance experiment using the e-puck robot. Experiments of this type are common in swarm robotics, but porting them to real robots is often challenging. By easing the development of complex behaviours on real robots, ASEBA both exposes collective robotics programming to a large community and opens new research perspectives for swarm robotics.