Not too long ago I found this under my drivers seat. Anyone have information on what this is, what use it serves, is it any good to a home mechanic, is it worth anything ? Couldn't find much about it through google or searching posts.

 

I'm just guessing but it looks like a VATs cracker. Once you have the right key, you'd use that to find out what resistor pellet the key would need.

Other then for a Key Shop/ dealer, I can't think of who'd want it.

 

Grumpy is correct, that is part of the unit called an interrogator that is used by GM and some locksmiths to interrogate the VATS control module to find the correct resistance value for the keys.