Front-end developers and designers can possibly use JSFiddle to do front-end prototyping and coding using mocked JSON. You can share the URL with your team. JSFiddle may not be the right tool for the job, but you never know. Axure seems to be getting popular. If we are using ExtJS, we should use ExtJS Designer (the code generated should be directly usable in your final product deployment)
Draft (an iPad application for HTML prototyping):
What is Pixate?
Pixate is an online tool designed to reduce the gap between designers and developers who work together on a same application project. Pixate gives you the ability to create complex UI animations and interactions for iOS and Android without writing a line of code.
To make an element interactive, you only need to choose the gesture you prefer from a panel and drop this on the element. Pixate provides seven default interactions/gesture: drag, tap, double tap, long press, rotate, pinch and scroll. You can then bind an animation to each interaction.
Another important feature of Pixate is the familiar use of layers which are extremely useful in managing different shapes and elements.
For me, what distinguishes Pixate from other similar tools is the simplicity of use: every aspect of the app can be quickly understood even by a non-experienced designer. Moreover, on the official site, you can find several video tutorials, some demos and a useful user guide which explains all the functions of the app.