.BT! File Extension
File TypeBitSpirit Incomplete Download File
What is a BT! file?
Partially downloaded file created by BitSpirit, a torrent downloading program; used for all in-progress downloads if the "Add .bt! extension to unfinished files" option is selected in the BitSpirit preferences under "File Options."
After a file has been fully downloaded, BitSpirit removes the temporary ".bt!" extension, and then the file can be used normally.
NOTE: BitTorrent, the original torrent client, uses the .!BT file extension for incomplete downloads.