The feasibility of run-time reconfiguration of FPGAs has been established by a large number of case studies. However, these systems have typically involved an ad hoc combination of hardware and software. The software that manages the dynamic reconfiguration is typically specialised to one application and one hardware configuration. We present three different applications of dynamic reconfiguration, based on research activities at Glasgow University, and extract a set of common requirements. We present the design of an extensible run-time system for managing the dynamic reconfiguration of FPGAs, motivated by these requirements. The system is called RAGE, and incorporates operating-system style services that permit sophisticated and high level operations on circuits.