Shortly after Internet Explorer 9 was released back in March, Microsoft began releasing Platform Previews of Internet Explorer 10. These "previews" don't include a user interface beyond a menu bar with a few essential options and therefore can't be used as a standard browser, yet there's a way to bring the engine from the Internet Explorer 10 developer previews to Internet Explorer 9's user interface.
Once the subject of so many jokes, Microsoft's Internet Explorer is experiencing a bit of a revival of late with IE9 being well received amongst Windows users. Now the Redmond outfit is unleashing IE 10, in Platform Preview 1 guise.
