aajm is a program that lets you watch a man juggle balls using ASCII art. You can adjust speed and styles and more.
Here is a related program that achieves the same effect but using a GUI. With JuggleMaster Deluxe, you can watch smooth juggling animations with colored balls to mesmerize yourself or to learn how to juggle.
JuggleMaster Deluxe is free and available in the Ubuntu repository. Search for jmdlx and install it using Synaptic or the command line. Then, run jmdlx in a terminal and be prepared to be amazed, wowed, and wondered.
The main menu at the top of the GUI contains the options needed to control the program. Just like aajm, you can select juggling styles, patterns, and siteswaps.
The features offered are more than mere entertainment. If you are serious about learning how to juggle, then this program is invaluable because you can slow down the speed to see hand placement and technique.