What are the keyboard shortcuts for navigating Modern UI apps?

Try Alt+← (also works to go back in explorer, and most browsers).

Here is the complete keyboard shortcut list for Windows 8, enter image description here

Also available at the official Blog for Windows 8.

Picture Location.

PageDown Scroll backward on the Modern Desktop Start screen

Alt + Shift + Tab Cycle backward through open windows

Shift + F6 Cycle backward through elements in a window or dialog box

Shift + Tab Cycle backward through elements in a window or dialog box

Ctrl + Shift + Tab Move backward through tabs

Backspace Display the previous folder in Windows Explorer Move up one folder level in Open or Save dialog box

For more keyboard shortcuts you can check out this post.

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