Many of the people in the world are using internet explorer for browsing web. but many websites does't look good in IE older versions. so a web developers and designers can check his website in ie tester, how its looks and how its works in all versions of internet explorer, internet explorer is the most common browser so your site should work properly in IE.
some tools of ajax does't work properly in IE so you can check them before using in website. its a good and nice tool where all versions of internet explorer are in one place.
Free Download IE Tester
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