From: Gordon Darling on
http://code.google.com/p/mergetorrent/

mergetorrent combines two or more partially downloaded torrents into a
single torrent that is more complete than either of the original
torrents.

Examples:
You start downloading the same torrent on two different computers and
each gets to 50% individually but probably not the same 50%. By combining
the results of the two properly, you probably already have 75% and may
have 100%.
You start downloading two different torrents that both include the same
file. Each gets to 50% on the common file. By combining the common file,
you probably have 75% already and may have 100%.

Using mergetorrent:

Just select the .torrent file and then select the two partial downloads.
mergetorrent will combine them accurately in seconds without a second
computer or even loading a bittorrent client.

GNU General Public License v3 (so the Hummy and Bloss scammers can sell
it!)

Regards
Gordon