From publisher blurb:
The Cepheus Engine System Reference Document comprises the core rules for a Classic Era Science Fiction 2D6-Based Open Gaming System. Inspired by the original three books of the oldest 2D6-based science fiction roleplaying game, the Cepheus Engine system incorporates elements of Open Game Content from previous releases of that game of intergalactic drifters and wanderers to create a basic system that will allow players and Referees alike to create their own science fiction universes or play in the ones they are already familiar with.
You'll find the core essence of your favorite sci-fi game here. You can explore interstellar space, make a ton of Credits on speculative trade, find yourself halfway across the sector after a serious misjump, or blow people up with your mind, if you can find training. You can even die during character creation. This stand-alone manuscript provides all the rules you need to play the game. The Cepheus Engine rules were intentionally designed to integrate well with other 2D6-based science fiction gaming systems, especially your favorite Classic Era modules and supplements. All of the material in the Cepheus Engine rules is considered Open Game Content.