Alex MacCaw is a Twitter engineer, O’Reilly author and open source developer. He has just released Stylo, which is an open source web app designer tool written in CoffeeScript and Spine. It allows you to manipulate various HTML elements, add styles and edit text.
You can draw shapes, apply shadows, background gradients and add a variety of other styles. Double click on an element to add text, and use keyboard shortcuts, such as command z to undo. In the latest versions of Chrome, you can even copy elements and paste their CSS into a text editor.
License: License Free