...They essentially do the same thing.
Select a source folder with some video clips (or several files in the
Mac version). The program will change the container to the selected
output without reencoding. For Windows, ffmpeg needs to be installed on
your system, it is included in the Mac download.
For a short video demonstration of the Mac version, go to:
http://www.youtube.com/watch?v=O278FHawa9k