Quick link into the introductory documentation: http://code.google.com/p/textfsm/wiki/TextFSMHowto — one specifies a state machine in a text template file that can include regexes and has a simple "->" syntax for state transitions.
On one hand, cool! On the other hand, uncool, if it encourages more people to have their programs interact with other programs via CLI parsing. We should be using APIs and libraries instead of working around the lack of them.