Otter App

Conceived by a Seattle developer as a way to reduce texting while driving, this GPS-enabled Android app knows when you're in the car and automatically intercepts/replies to incoming texts; non-driving usefulness comes via manual mode, which gives you a choice of personalized push-button responses, and a timered auto-reply mode that'll send a custom text when you're say, stuck on a plane for five hours or spending just as much time having sex! Probably even more than that, though, that's just a conservative estimate.