IETester is a free web browser specifically designed for testing web sites in Internet Explorer including IE 8 beta, IE 7, IE 6, IE 5.5 on both XP and Vista.
Like any web browser, IETester has the usual forward and back buttons, refresh, stop, home, and favorite buttons, but it also has a special feature that allows you to launch new tabs which render the web site in different versions of IE. With IE8's public beta just around the corner, web site owners need to verify that their sites are going to display properly in the new browser, which runs in standards-compliant mode by default. You can download IETester for free (donations accepted) from here. (via Ajaxian)