Here are the most important things to remember:
1. In general, the universe is the same (except as described below). So we have the same physics, alien races, very similar governments, technology is the same, etc.
2. The history and timeline are completely different. So if the year is 1240, and you know something happened in the year 1239 of the "official" traveller universe, then that thing did not happen in this universe.
3. Details of governments are different.
If you don't know about the Traveller Universe......
You probably should read up on the "Classic Traveller Universe and History" on the web.
Here are the most important things to remember:
1. Spaceships work, but they take a week to get between stars (and only nearby stars).
2. There is no faster than light communications, so messages go no faster than spaceships.
3. Long ago, humans (and terran plants and animals in general) were distributed to a large number of planets all over our galaxy, and civilizations sprung up all over, each isolated from each other. Most people believe The Ancients (an old, powerful, highly advanced race) did this.
4. There are intelligent aliens.
5. There is a large, human-dominated empire called "The Third Imperium", as well as other large single-race governments, and several smaller political units.
6. Here are some other general introductions to the Traveller Universe:
- https://en.wikipedia.org/wiki/Traveller_(role-playing_game) (Especially the "Game overview" section)
- http://www.drye.ca/hans/Handouts.htm Only the "Ancients" part of this file applies!
Minor Points about My Traveller Universe
The rules about guns differ widely from planet to planet, and sometimes from region to region on a single planet. However, you can always carry any weapon (except some Naval ship to ship weapons) in your ship's locker. If the planet doesn't allow them, you can't take them off your ship. In a few very rare cases, you can not take them out of the ship's locker, but you can always store them there, while you are on a planet.
In the official traveller universe the third imperium is huge, but in my traveller universe it is much smaller. Although it is bigger than it's immediate neighbors, it is only three or four times as big. Also, there are large reaches of space that are poorly explored and lightly settled. This is quite different than the official traveller universe.
There are a lot more aliens common in my universe, than in the traveller universe. (At a minimum, expect GURPS Aliens, and many aliens (and some planets) from the Star Wars role playing game.
Historical Events in My Traveller Universe
Either one of these wars can serve as historical background for your characters (for those that need wars in their background :-)
The Fourth Frontier War
The most recent large scale war was the Fourth Frontier War, which was a major war between the Zhodani and the Third Imperium. There was a vast amount of fighting and death and destruction, and in the end, the boarder between the two was redrawn very near to where it was before the war.
The Arden War
Just after that war, was another, much smaller war called the the "Arden War". Basically, Arden is the head of a small confederation of Zhodani client systems (not in the Zhodani Consulate). Very near their systems, but not part of their confederation, were several small, independent star systems which had good relations with the Imperium. After the Fourth Frontier War, both groups of planets were in neutral space between the Zhodani and the Imperium. However, Arden thought that they could take over the systems one by one, and tried to do so.
The systems started out all independent, and initially Arden was able to take over one, but that unified the nearby systems against Arden. This unification, together with many volunteers (and a little direct help) from the Imperium turned the tied, and Arden was forced to relinquish the territory they had taken over in the early part of the war. Most of the actual fighting took place around the gas giants of the sytems. The most famous battle of the "Typier Massacre" when an entire outpost of a religious order on a gas giant moon, was wiped out.
In nearby imperial systems, it was widely rumored that the Arden military had tried to redirect Oort cloud comets for planetary bombardment purposes. But this was never confirmed, and no actual use of comets was made during the war.
Members of the Arden Alliance include Arden, Zenopit, and Tremoot Dex (from where most attacks were made) and Quare (which was an important intelligence, spying, and raiding center).
The independent systems included Rangent (which was captured for a time), Tionale, Phlume (both locations of major battles), Edinina, Digitis, and Stilleto.
There are also ongoing battles with pirates all over the place.
And also large and small scale wars in other, distant parts of the third imperium.