"Protovis composes custom views of data with simple marks such as bars and dots. Unlike low-level graphics libraries that quickly become tedious for visualization, Protovis defines marks through dynamic properties that encode data, allowing inheritance, scales and layouts to simplify construction.
Protovis is free and open-source, provided under the BSD License. It uses JavaScript and SVG for web-native visualizations; no plugin required (though you will need a modern web browser)! Although programming experience is helpful, Protovis is mostly declarative and designed to be learned by example."

'Below is a “getting started” tutorial, a helpful autotesting plugin, and hints about a TextMate bundle for Javascript Unit Testing and a future Peepcode on Javascript Unit Testing.'

Considering techie solutions to some simple problems....

Updated site

Impressive hands-on demo of Mootools Javascript libraries.