JTrack is tracking software for juggling props.
It uses a linear Kalman filter to track juggling objects on the screen through time, mapping their trajectories.
Once the ojbects have been tracked, there are many different effects and visualizations that can be created from the data. The Kalman filter tracks acceleration, velocity and position in both the x and y plane. It's really good at tracking parabolic motion; that's highly predictable movement.