This program reads a file, looks for different file types (specified in a external file) inside it, and creates a new file for each file found. It may not sound very useful right now, but you can find fun stuff inside games' data files with it.
Anyway, get it here. On unix, just grab the .tgz. On windows, grab the binary and deconcat.conf.
Read the README file included for more information.
PS: this is a command line tool.