Pingendo is a free WYSIWYG application for prototyping web pages. It uses Twitter's Bootstrap as a base, and supports responsive web design (your sites will automatically adapt to fit phones, tablets, laptops and desktops).

Getting started is as easy as dragging and dropping. Organise your layout with sections, columns, rows or containers; choose components like lists, panels, tables or forms; choose a navigation method, write some text, insert a few buttons, present images in various ways (a single picture, thumbnails, a carousel), and add media objects including YouTube videos and Google Maps.

Click an object like a paragraph and you can add your own text, change its properties from the Settings panel (alignment, text colour etc), maybe opt to hide the object in one or more version of your site (display something to desktop visitors, but not on phones).

There's also support for live HTML/ CSS editing. Click an object to jump to its code, edit it, and the preview updates as soon as you're done.

Or maybe you prefer to edit your components in something else? No problem, because the program also detects when its HTML, CSS or images are changed, automatically reloading and previewing the results.