I am very happy with the Ultramodern4 OGL. Despite some minor typesetting issues and typos (the most notable being "d28" in several places where it should be "2d8", this is a quality product full of useful game info. As far as I know, it has all the crunch and at least some of the fluff from the full-game product. You do need a copy of the 4th edition D&D Players Handbook or D&D Essentials Rules Compendium to use the OGL in a game.
[4 of 5 Stars!]