From the app listing:
Thrifty Car Rental is one of the most widely recognized brands in the travel industry. Thrifty is a value-oriented car rental company that has a significant presence both in the airport and local car rental markets around the globe.
The app does have a primary focus on the American market, and of course has a rather narrow appeal, but it is apps like Thrifty that are going to help the adoption of Windows Phone as a platform. I'm happy to see the full use of the Windows 8 User Interface, as opposed to a web page based application, being used here.
People now expect a wide range of functionality in their applications. Every notable company that comes to Windows Phone (alongside iOS and Android) legitimises Microsoft's platform and will encourage more companies to jump to Windows Phone. Once on the WP platform it's only a short step away from having the apps also appearing Windows 8 and Windows RT, and of course apps on those platforms are only a skip away from appearing on Windows Phone 8!
You can pick up the free app from the Windows Store, or the AAWP App Directory.