The Samsung Galaxy Note 2 multi-window feature started off lacking much functionality, but has since gotten rather useful. If you don’t know, multi-window allows Note II owners to use two applications simultaneously. The first app populates the top half of the screen, while the second populates the bottom half. Now, Galaxy Note 10.1 users can add multi-window functionality to any app.
XDA Forum Member Leppin released a tool for Windows that automatically adds everything needed. This is actually different from the other methods, which change system files so that any app can be used. While it may take longer, users don’t have to worry about messing up other system modifications to get the multi-window mod working for all apps.
The process is pretty simple. Users download the tool and grab the APK they want to modify off of their device. They then run the APK through the tool. Once done, they put it back, install it, and restore data. That application should be usable in multi-window after that. A nifty thing about this process is that users can create packs of apps that are multi-window compatible for future use in ROMs.
For more details, check out the original thread._________