Simulators are in fact programs that make some little guys juggle on a computer
screen. When it comes to passing correctly, there are not a lot of them (would
that be like in real life ?), and the winners are JoePass! and Jongl.
JoePass! is more used throughout the site, but that's only because I discovered it before Jongl. I recommend trying both of them. JoePass! has some very convenient features for creating your patterns while Jongl offers some nice output on the screen.