Information based on AppIndex.com and Wikipedia:
With a C# shared codebase, developers can use Xamarin tools to write native iOS, Android, and Windows apps with native user interfaces and share code across multiple platforms. Xamarin has over 1 million developers in more than 120 countries around the world as of May 2015.
The software underlying PhoneGap is Apache Cordova. The software was previously called just “PhoneGap”, then “Apache Callback”. Asopen-source software, Apache Cordova allows non-Adobe wrappers around it, such as Intel XDK or Appery.io.
iFactr provides the only mobile platform that supports both legacy and modern Windows as well as iOS and Android. Whether building new apps or modernizing existing systems, iFactr was designed from the ground-up for mission-critical enterprise line-of-business apps, providing rich, native experiences for every platform and support for critical sensors on rugged devices like barcode scanning and geolocation.
Qt is a cross-platform application development framework for desktop, embedded and mobile. Supported Platforms include Linux, OS X, Windows, VxWorks, QNX, Android, iOS, BlackBerry, Sailfish OS and others.