The jQuery HTML5 Audio Player with Flash Fallback.

jquery replacesvg

this is a simple svg replacement plugin.

jQuery SVGMagic

A simple jQuery plugin that creates a fallback for .SVG images (backgroundimage supported to!). In case your browser doesn’t support .SVG images it will create a .PNG file and replace the .SVG with it. This means that you don’t have to create two versions of your images to support IE8 and lower.

jQuery CSS Fallback Plugin

This plugin provides a fallback, for example, if you use a CDN for a CSS file.