What is a BTAPP file?
A BTAPP file is an application that has been developed for the TORRENT download program uTorrent. It is essentially an app for uTorrent that can access all the functionality of the uTorrent client. These apps can be added to the uTorrent client from within the application. This will install the app in uTorrent client and provide all the functionality of downloading TORRENT files.
BTAPP File Format - More information