It turns out that SVG, a web standard for displaying scalable vector graphics, has been quietly growing in popularity and use since last time I was paying attention.
Basically, you call the JS library to do SVG stuff, and if the visitor who's viewing your page is using a browser that already supports SVG, then the library passes the command along to the browser so it can use its native support. If the browser doesn't support SVG, then the JS library executes the SVG command itself.
The result is that about 95% of all browsers can view SVG content if the person who created the page used svgweb, even though Internet Explorer doesn't support SVG natively. This is super cool.
For a bit more info, watch the following one-minute intro video, including a few demos (if you don't see a video here, just follow that link):
For more details, see the 45-minute YouTube video of a talk given recently at Google: SVG Web Library and Open Web Advocacy. (Seeing that talk at work the other week was my first exposure to SVG Web.)
The svgweb page also provides several demos you can try out in your browser to see this stuff in action.
Regardless of anything to do with SVG, this paradigm amazes me: some browser doesn't support some web standard? Implement the standard in JS and provide it as a library!