Not free, but one very widely used tool for analyzing and improving Process Performance Models (PPM) using Monte Carlo simulations:
Quoting:
"Oracle Crystal Ball is the leading spreadsheet-based application suite for predictive modeling, forecasting, simulation, and optimization. It gives you unparalleled insight into the critical factors affecting risk. With Crystal Ball, you can make the right tactical decisions to reach your objectives and gain a competitive edge under even the most uncertain market conditions.
Using Monte Carlo simulation, Oracle Crystal Ball automatically calculates and records the results of thousands of different "what if" cases. Analysis of these scenarios reveals to you the range of possible outcomes, their probability of occurring, the inputs that most impact your model, and where you should focus your efforts. Oracle Crystal Ball is for strategic planners, financial analysts, engineers, scientists, entrepreneurs, CPAs, marketing managers, venture capitalists, consultants, six sigma professionals, and anyone else who uses spreadsheets to forecast uncertain results."
