jBPM has been an early adopter, supporter, and implementer of the Business Process Simulation Interchange Standard (BPSim). We believe that BPSim (which is a WfMC standard) will create a wide adoption of business process simulation in the BPM community, and are very happy to be part of that effort.
With the BPSim version 1.0 recently released, we have updated our jBPM core engine, simulation engine (which is based on the core engine) and our web-based tooling (jBPM Designer) to this latest version of the specification.
If you are interested in learning more about BPSim and jBPM or just have any questions feel free to talk to us on our IRC channels.
Here is the link to the jBPM Designer business process simulation capabilities that Tihomir posted before. We are adding new features and usability enhancements to it that should be out soon, so stay tuned.