At this time there is html5shiv, dean edwards ie7-js and modernizr.
- html5shiv allows you to use the new HTML5 tags in versions of IE that don’t understand them. Without it, IE will choke on these tags, so you need this if you intend to use the tags. Don’t expect it to make the tags actually do anything in IE though! It just stop the browser complaining about them.
- modernizr sets a bunch of classes in your HTML, depending on the available features, which you can use to change your layout according to what the browser supports. It also allows you to use the new HTML5 tags in IE, like html5shiv.
- ie7.js (as well as ie8.js and ie9.js) uses Javascript to retro-fit some missing functionality to IE.
There is also another tool that helps make things all happy in IE 6-9.