RatDVD

RatDVD offers a way to compress an entire DVD (including menus, chapters, extra audio, etc) into a very small package. Once installed, a variety of programs can play back the RatDVD compressed files. And if you want to play it on a regular DVD player, it always contains all data required to reconstruct a "regular" DVD playable in any player. While I haven't tried it yet myself, it sounds very impressive.