Ford has had options like this forever and it's usually targeted at farmers and ranchers, I think the first I've found was like a 77 or 78 f250 'rancher' that had a generator option on the main belt off the motor. The adds show a guy cutting boards with a skill saw to mend a fence or something.

I almost purchased that truck, but I needed a higher cargo capacity for my travel trailer, and the added batteries reduced it by 250lbs or so. The ability to plug a travel trailer directly into the truck and run it is really cool.