Foundation: Others who said the book was a collection of novellas are correct. I'm on the fifth section, the last section. The novellas are not connected by story or characters--only the theme of the Foundation.
I found the first three stories the best. I wasn't that enthralled with the last one. It seemed to me to be the least connected of the four sections I've read.
As for Traveller, the last two stories are using the term "Trader" in the same way that we use "Traveller" in game. They are a group of special people who live in space, between the stars, while almost all others are ground based on the various worlds.
And, the last section--the last story--is called The Merchant Princes.
The stories were original written in the early 1940's, and published in the 1950's. I can see the ideas in the book, which are commonplace now, be something to behold back then. Sometimes, the language gets to me: for example, Asimov uses "atomics" quite a bit when we would say today, "nuclear". Some of the "high" tech, too, where a character remarks that another character, from a lower tech world, was not aware of a high tech microfiche recorder.