The Metro UI has been very popular since the release of Windows Phone 7. Lots of apps and themes have been released based on this UI. The latest one to release is a nice Windows 7 theme based on this UI. Windows Metro UI theme is a free theme for Windows 7 which brings in the look and feel of Metro UI to Windows 7. This theme combines the look and feel of MetroTwit (Twitter app), Zune and a little bit of Windows 8.
The theme really looks awesome with the changes it makes to Windows explorer, start orb and other UI. The theme requires you to patch system files for installing, you can refer our guide on how to install custom themes on Windows 7.