Cacoo

Cacoo is an application for drawing a variety of diagrams. It allows to create site maps, wire frames, UML, network charts, floor plans, and many other types of diagrams with ease. Cacoo includes a wide variety of stencils for various purposes. Multiple users can edit a single diagram at once - changes are shown on the sharers screen in real time. Diagrams can be embedded into blogs, posted to Twitter, Facebook, Google Buzz, or shared via URL (if you make them public). You can export results to PDF, PS, SVG, and PNG formats. An API is available for developers who wish to interact with Cacoo from their services and applications.