OpenDarkEngine

Well, I understand that the dark engine was based primarily around the quake engine. Just how much is the dark engine LIKE Quake? I mean, they obviously are similar in that they use a skybox, and that objects and characters are limited to what is made within the playing field. Also, just how much time did it take to discover the file system for dark? Am I making an understandable statement that appropriately describes the system which makes up dark.