Some trips are well planned; others happen on a whim. For the whimsy in you, there's Zipcar, which offers its members quick, cheap, hassle-free car rental on short notice. So when your afternoon meeting is canceled during a business trip to San Francisco, your boss may sulk and head back to the hotel, but you can be tooling around Napa in a Zipcar. The Zipcar iPhone app amplifies the quickness and ease of this process. Beyond helping you manage reservations, find nearby pickup locations and browse car models available, the app offers clever capabilities like remote locking and unlocking and honking your car's horn from your phone when you inevitably forget what it looks like in a crowded lot.
Zipcar app: free