There are plenty of applicatios but I would go for top three here

RhoMobile – RhoMobile offers Rhodes, which is an open-source framework based on Ruby. This permits the developer to create native apps, spanning over a stunning range of OS’ and smartphones. The OS’ include Android, Windows Mobile, Symbian, iPhone and RIM, which pretty much covers it all.

The framework supplied by RhoMobile is such that you only need to code once. This code can be used to build apps for most of the major smartphones. Native apps are great for working with available hardware, so your job gets done with ease, speed and accuracy.

RhoMobile also offers developers RhoHub, which is a hosted development environment, and RhoSync, which can be employed as a standalone server to keep all the app data current on the users’ handhelds

PhoneGap – PhoneGap, which won great acclaim at Web 2.0 Expo San Francisco’s 2009 Launch Pad event, is an FOSS environment that allows developers to create apps for Android, Palm, Symbian, BlackBerry, iPhone, iTouch and iPad devices. This platform uses standard web development languages such as HTML and JavaScript.

PhoneGap allows the developer to work with device hardware features such as accelerometer, GPS/location, camera, sound and much more.

Whoop – This one, though not really a top tool, is interesting. Whoop confidently states that they are “The one-stop mobile app publishing platform for non-developers”. Even if you are not a developer, you can still get some cross-formatting done with Whoop. The Whoop Creative Studio is basically a WYSIWYG editor that lets you easily drag and drop mobile app elements onto it, to achieve desired effects. What is more, you can even export your app in many formats, depending on the OS, including Windows Mobile, BlackBerry, Android, iPhone and more.

Source: EXORUM