Internet Explorer is a special case to web design testing because of three things. First, some versions have unique bugs; second, it is a very complex task to have two versions of the browser run side by side on the same Windows machine; and third, you must test everything in it because it is the dominant browser out there. The task just got easier with IE Tester.

This tool is available for free and shows your HTML and CSS in four different versions of IE: 8 beta, 7, 6, and 5.5, on both Vista and XP. It emulates both the rendering and javascript engines of the browsers. While IE Tester runs smoothly, it is still in an early development phase and there are several known bugs. Development is ongoing, the current version is 0.2. The install package is about 24MBs in size.

The same site also offers for download DebugBar, a web development toolkit for IE.