The British Isles Traveller Support group produce a number of useful GM aids in the time-honoured A5 supplement booklet format. One of these, At Close Quarters, is essentially an updated version of the AHL combat rules, but with a bit more complexity/realism.
Agemegos, I'm intrigued by your statement about GURPS Space having a more detailed and realistic SysGen than First In.
I've intended for a while to get a copy of FI for its SysGen, now I'm not sure. I only want to buy one of them, and the systems need to be Traveller compatible as well as detailed and realistic - which would you (or anyone else, please) recommend?
Both systems are by Jon Zeigler. GURPS Space is seven years more recent, and is correspondingly more highly developed. For instance, it takes into account the brightening of stars as they age. The big difference is that GURPS Space has a really ingenious way of dealing with the relationship between gravity, world size, temperature, and atmospheric composition (which is dictated by a mechanism called "Jeans escape"). I consider it a stroke of genius. In that respect, it is the most realistic star system generator around: nothing else touches it. It also has a clever backwards-or-forwards feature, which lets you design the planet you want and then let the system insert it into the star system in a physically realistic place.
However, the system in First In has rules for classifying planets' characteristics to produce Traveller UWPs, and GURPS Space doesn't mention them. It's not hard to work out, if you know what the codes means, but without some sort of Traveller product you won't know what the codes mean.
And I have to say, the system in GURPS Space is more complicated and time-consuming. I ended up designing a spreadsheet to do the calculations for me.