In this paper, we present the proposal and implementation of a Java-based parallel discrete-event simulation tool for cluster computing called ClusterSim (Cluster Simulation Tool). The ClusterSim supports visual modeling and simulation of clusters and their workloads for performance analysis. A cluster is composed of single or multi-processed nodes, parallel job schedulers, network topologies and technologies. A workload is represented by users that submit jobs composed of tasks described by probability distributions and their internal structure (CPU, I/O and MPI instructions). Our main objectives in this paper: to present the proposal and implementations of the software architecture and simulation model of ClusterSim; to verify and validate ClusterSim; to analyze ClusterSim by means of a case study. Our main contributions are: the proposal and implementation of ClusterSim with an hybrid workload model, a graphical environment, the modeling of heterogeneous clusters and a statistical and performance module.