Originally released as part of Free RPG Day 2008.
From the back of the book:
Traveller is back. Based on the classic original and updated for the new millennium, within these covers you can find everything you require to begin exploring the vast Third Imperium and the alien-controlled regions that surround it -- or any other science fiction setting you can imagine!
Traveller Book Zero is an introductory booklet designed to give players an understanding of the rules and mechanics in this latest incarnation of the classic science fiction roleplaying game.
This book contains all you need to create characters, equip them and send them on interstellar adventure.
Whether you are new to Traveller or an old hand, the science fiction adventures you desire await within.