New this build is the ability to export Windows 8 Metro apps! For more information see How to make a Windows 8 Metro app. Please note the Windows 8 App Store is currently closed, so this option is just for testing since a new OS and browser are involved (HTML5 based Metro apps run using Internet Explorer 10). However, it should also help you to be ready as soon as the App Store opens. Give it a spin and be sure to report any issues you come across.
Reminder: this is a beta release, intended for testing. If you do not want to risk having new problems we recommend sticking to the last stable release, which is currently r80.2.