mpqfs (or MoPaQ Filesystem) is a FUSE filesystem for Blizzard Entertainment's MoPaQ (.mpq) archives. With it, you can use regular system tools and applications such as Finder and QuickTime Player or standard UNIX programs to access the content of such archives.
MoPaQ archives have been used by Blizzard Entertainment since the original Diablo to store game assets.
mpqfs is powered by MPQKit, an object-oriented framework for manipulating MoPaQ archives. For details on the project, see http://www.devklog.net/mpqkit/.