There are plenty of Monte Carlo-based scheduling tools (including downloadable Excel spreadsheets) but all of them require the different project parts to be input separately (because they have no assumption of being hooked up to an existing project management system) which seems like a royal pain in the ass so they probably get downloaded and hardly used.
And probably Fog Creek's implementation is better anyway.
I would probably use FogBugz if its usability was better. I think a breadcrumb and a sidebar would help.