Originally Posted by Wikipedia
ratDVD is a highly compressed file type, containing all the contents of a Digital Versatile Disc (DVD) movie. Files compressed by ratDVD are usually one to two gigabytes in size. It is currently available only for the Microsoft Windows Operating system.
ratDVD works by compressing a full DVD into a .ratDVD file and then playing its contents by decompressing the file and using a DirectShow-compatible DVD player.
ratDVD was only a preview version of the now commercially sold fluxDVD. While ratDVD contained the features that allowed the home user to create their own archived DVDs, this function has been removed from fluxDVD, allowing only content owners to make and sell fluxDVD archives.