Research community on distributed systems, and in particular on peer-to-peer systems, needs tools for evaluating their own protocols and services, as well as against other protocols with the same precondictions. Since a (TCP/IP) experimental evaluation is not always feasible, simulation tools appeared. In this paper we introduce PlanetSim, a discrete event-based simulation framework for overlay networks and services, as well as extensions from third parties that prove its true extensibility and adaptability to the reserarchers' needs. In addition, we introduce within PlanetSim a novel way of implementing peer-to-peer overlay protocols based on behaviors. Categories and Subject Descriptors I.6.8 [Types of Simulation]: Discrete event ; D.4.8 [Performance]: Simulation, Measurements; D.3.3 [Language Constructs and Features]: Frameworks General Terms Algorithms, Measurement, Performance, Design, Experimentation Keywords Overlay network simulator, discrete event-based simulation, frame...