The Niclas van Rijn/David Falkayn stories (Poul Anderson - Technical Civilisation)
Currently out in reprint as collections in 3 books. They are a bit more heroic than the typical "Traveller" is IMHO but show a lot of background on Merchant Princes, Interaction of powerful Merchant Houses and/or Governments and a society that is speeding towards Stagnation. The Polysotechnical League has a bit of late Vilanie and/or Ramshackle Empire to it (minus nobles IIRC) and could be used as a template for a "Imperial Twilight" campaign set late in the 2nd Empire
Useful as background stuff and in some cases for scout/exploration elements, less so for a trader campaign
The Domenic Flandry stories (Poul Anderson - Technical Civilisation)
Up for a reprint / currently reprinting in compilation format
Same Universe as above but a lot later in time. The collaps of the League, the sacking of Earth are all things in the past. Earth is strong again and rules an Empire, complete with Emperor. The feeling of the stories vary from "distant and uncaring Empire" in the early novels to "Decaying giant" in the latter stories. Partially since the main hero rises in position and gains more insight, partially since the universe expands. The feeling is Classic Traveller seen through the MegaTraveller/TNE lense. Flandry is a Troubleshooter in the Mold of the classic victorian hero, putting out fires so he can seduce another mistress, relish another old Cognac and have a good life. The Mersains are a good stand-in for Zhodanie and Solomanie and both powers are hurling towards Mutual Assured Collapse.
A good source for espionage and in the later books for court intrigue and crumbling empires/rebellion.
The CoDominion Stories (Jerry Pournelle - Future History)
These are actually three sets of novels:
"The Mercenary" deals with the actions of a Line Marine batallion that later turns Mercenary. A good source for a Merc Campaign that aims for more than combat. Shows us contract negotiations, civilian and NCO influence and the problems with Mercs and fighting
"The Sparta Trilogie" (Prince of Mercenaries, Go Tell the Spartans, Prince of Sparta) deals with a Merc campaign against well supplied, well trained terrorists/freedom fighters that have outside help, political backstabbing, semi-independent planets and the limits of independence and mixed technical capabilities. While the tech is more 2300AD than Traveller (no Contra Grav, no Thruster Plates) the overall mix works out. Use for background information, more so if you use the MT/TNE "Dark Empire"
"The WarWorld Stories" are some of the short stories that deal with Haven, a remote colonie that gets deportees dumped on it by everyone with some influence resulting in a patchwork culture. Most WarWorld stuff is later, either during the 1st Empire or during the recovery/2nd Empire but some are set in CoDo Time. Mostly useful as a background for exile/prison planets and systems that use those worlds
The Moat stories (Pournelle, Future History)
Set some centuries after the CoDo era. Humanity has destroyed it's homeworld, build a new Empire centered on Spartha, destroyed that Empire in a Rebellion and Re-Build another one, again based on Spartha. Now it has it's first contact with an alien civilisation.
The Aliens itself are the least useful part since they are non-FTL when contacted. More useful is the start of the book explaining rebellions, suppression, the noble system and it's problems etc. The second book had some interesting concepts in SciFi Tech (basically PDA's)
The War world stories (Pournelle and others, Future History)
The 1st Empire of Man ends in a bloddy rebellion when the Saurons and their allies rebell against Spartha. There are some good short stories about the Rebellion itself with ideas of strategies in space, reasons to attack planets and most important politics within the fleet and the two power blocks. The Saurons would make an interesting Solomanie variant taking the "True Human" idea one step further with selective breeding, caste system and above baseline human troops.
Later WarWorld Stories center on Haven as it is conquered by the surviving Saurons. Good material if you ever run a TED campaign in the TNE setting because that's what the Saurons become. The stories cover a few centuries from the conquest days to the occupation to the rebellion of the Havenites.
