It's an iPhone game. In a bizarre sequence of events, this portable entry in the Borderlands series appears to have been leaked by the digital version of the Borderlands 2 Official Strategy Guide. The following advertisement appears in it, apparently detailing a new iOS-exclusive entry in the series, starring the original cast of characters:
Above: A screengrab reportedly taken from the iPad edition of the Official Strategy Guide
Sadly, there are no screenshots of actual gameplay, so whether this is a first-person shooter or not remains to be seen, but that features list sounds very promising anyway. There's one thing we wish we were doing when we're not playing Borderlands 2, and that's playing Borderlands 2. Perhaps this will help fill that daily void.
More as soon as it's more official, which should be pretty soon considering there's only a week or so left of October.