From publisher blurb:
D4Core is a universal, interchangeable Role Playing Game system. D4Core is not a rigid set of rules that you must adhere to in order to play. Yes, there are some mechanics to the game that will “power” your adventures but for the most part play is open ended and lends itself more towards the use of House Rules(variations to the rules that gaming groups like to play and agree on). There is no wrong way to play the game.
D4Core is meant to a fast and easy system for a quick night of gaming, but robust enough to handle a long campaign. The emphasis is on having fun and not get bogged down with complicated rules. As I said before there are some core mechanics, but elements can be mixed, matched, or eliminated based on whatever works for your scenario.