@RISK - @RISK is the world's most widely used risk analysis tool.
RiskAMP - RiskAMP is a full-featured Monte Carlo Simulation Engine for Microsoft Excel.
Zingtree - Build your own question & answer style troubleshooters
Yasai - YASAI is an open-source Monte Carlo simulation add-in for Microsoft Excel
TreePlan - TreePlan helps you build a decision tree diagram in an Excel worksheet using dialog boxes.
MC FLO - MC FLO is a add-in which make it easier to make decisions using the Monte-Carlo simulation approach.