Is there a decent and downloadable comet/asteroid impact simulator?

Like a 3D application, not those cheap calculators that you jut type in info on the "impact" and it doesn't show you how it hit. I am asking because I saw this thing on the History channel about asteroids and comets, and this woman was using a application to show the shock-wave,impact,the status of the impact, all of the good stuff.. really don't have time to search over the internet for several hours at a time looking for something so simple...Please tell me what may be what I'm looking for.