GraphWalker is an open source Model-based testing tool for test automation. It's designed to make it easy to generate your tests using models.

Few useful informative videos which describe the MBT approach

Literature which may help to understand the MBT approach

MBT example by Harry Robinson
Plenty of articles and presentations on Harry Robinson web site
MBT by Microsoft and Spec Explorer
Model-Based Testing Essentials, a quite informative and good for understanding book
MBT overview