Hilton HHonors is a free mobile app for the many Hilton hotel chains, including not just Hilton but DoubleTree, Embassy Suites, Waldorf Astoria and more. The app combines a range of different functions relating to these hotels. For instance, you can book hotel rooms online via the app, getting special deals. You can also check in, order room service, request extra pillows and even use your mobile device as a smart room key. It also displays local weather information as soon as you check in.