Behavioral animation has been used to animate flocks, schools, herds, and crowds. All of these require interaction between a large number of "characters" with relatively simple, rule-based motion. Fabric can also be simulated using behavioral techniques.
Example 1: single beast, static object repulses, food attracts
Code - Movie
Example 2: multiple beasts, repulse plus center attract
Code - Movie
Example 3: multiple beasts, repulse, center attract, turn limits
Code - Movie
Example 4: same as 3, plus stochastic elements
Code - Movie
Example 5: dynamic target (simple flock/herd/school)
Code - Movie
Example 6: tag -> beasts with dynamic state
Code - Movie
The particle system example has been modified below to handle the orientation of the actors, as well as the interactions between them: