Adobe AIR!

kodeWeave is a realtime coding playground for HTML, CSS and Javascript. Similar to JSFiddle and JSBin, but kodeWeave was made to work offline but also as a prototyping application to build applications for desktop operating systems while on mobile devices. (PhoneGap Build is recommended for mobile devices)

Appcelerator Titanium, offered for free by Appcelerator, lets web developers use web technologies, open source and cloud computing to build native apps for iPhone, Android, Windows, Mac OSX and Linux.

Convertigo is the most advanced Open Source Mobile Application Development Platform for Enterprises, featuring all the required components needed to develop and to run cross-platform mobile enterprises application connected to enterprise's back-end business applications.

Codename One provides a comprehensive solution for WORA (write-once-run-anywhere) mobile app development. You write the applications in Java using and deploy the application to Android, iOS, Windows Phone, or other platforms. The resulting app is a native app (not HTML5).

Sencha Touch allows you to develop mobile web apps that look and feel native on iPhone, Android, and BlackBerry touch devices.Free & open source license available for open source projects.

Worklight helps you build, test, and deploy native, HTML5, and hybrid mobile apps for Android, iOS, BlackBerry, and Windows Phone devices. The free Worklight Developer Edition gives you tools and an app server—in an easy-to-install Eclipse plugin.

Use your web skills to write NATIVE apps once and build for ALL smartphones with Rhodes, the industry’s first smartphone app framework

Mobile App Development Platform for non-developers: create native apps; send to devices or submit to app stores; manage apps from a secure CMS.