PhoneGap is a mobile development framework that allows mobile developers to build applications using Javascript, HTML5 and CSS3 and deliver applications to multiple mobile operating systems such as iOS and Android.  The applications created are not truly native as they use HTML5 and CSS3 for the front-end rather than the platforms native UI framework, but they are still applications that can be downloaded from the App Store or Marketplace.

One of the challenges of mobile development is building the same application for each operating system and maintaining it as the application evolves and as the operating systems are updated.  With a mobile unifying technology like PhoneGap or Xamarin, many of these challenges are managed.