The ever-awesome Bundle of Holding is featuring The Clement Sector from Gyspy Knights Games. The Clement Sector is a great small-ship universe setting for Cepheus Engine RPG, or the 2d6 Sci-Fi RPG, better known as the real modern version of the Traveller RPG (not the overpriced Mongoose edition). The Explorer Starter Collection includes Clement Sector: The Rules and is a great way to get into the ruleset.
Wargaming, Boardgaming, & Roleplaying
Rocky Mountain Navy Gamer 
I wholeheartedly endorse this, the Clement Sector is a well-documented and thought-out ATU using the Cepheus Engine rules. Tons of supplements and source material to dip into!