A set of rigged tank tracks (and a low-poly vehicle to go with them). The rigging is done using vertex parenting, constraints, and a Curve modifier. To use the rig, simply drag/rotate the master parent (cube).
This was created for a tutorial on CGCookie.com:
NOTE: This model is released CC-BY-NC-SA; it's intended for educational use and may not be used commercially without prior approval from CGCookie.com.