Tkar aims to be the gnuplot of animation — a quick and dirty way to get
data from a stream or file into a window to see what is happening. It is
more suited to animating discrete objects rather than numerical
functions or arbitrary datasets. It would be ideal for visualizing
output of a multi-agent simulation, for example.
Tkar is now a gem on rubyforge. Previously, it was a single-file
executable. The only dependency is Tk/Ruby.
Tkar also functions as a simulink block, analogous to the plotter block
and superior to simulink’s native animation features. (You need to
compile a simulink plug-in.)
Here is a movie made from one of the examples:
(tkar has rudimentary support for creating such movies)
 this particular animation is from a tool for visualizing vehicle
safety systems in which tkar was used. The tool was developed for an
automotive company that citizens of my country are now part owners of.
Tkar itself is free software under the ruby license.