It is loosely based on a system that i've thouht of and have playtested with my group a couple of times. It has never been properly written down before as many parts have been subject to change from session to session, and it has before been very dependent on other game's rules to function properly. The Shadow of the Citadel is on the contrary a fully developed system, at least as developed as is possible in 48 hours. The system is also influenced by the amazing game Coriolis; the third horizon by Free League. It uses a D6 system based on rolling 1:s, just like The Shadow of the Citadel. I have however resorted to using D4: s and implementing the Difficulty system.