Windows 8 Metro Application Installation Folder

Metro applications are stored in C:\Program Files\WindowsApps. But you can't access it directly. You have to set show hidden folder in folder option first. After that, you must take the ownership and permission.

How to take ownership in Windows 7 | 8

If you want to see list of application, copy-paste this address to the address bar:
explorer.exe shell:::{4234d49b-0245-4df3-B780-3893943456e1}