This game is kickass! It engages your brain - memory and planning are paramount - while also having an excellent American folk soundtrack of guitars and harmonicas. Daft numbers of scenarios & campaigns, all with inherent replayability, can be boosted to astronomical proportions (https://codeload.github.com/oseparovic/RRT2Maps/zip/master
<< that's a metric f*ck-tonne of extra maps & scenarios). I have a thing for older games - they tended to be more demanding and more mentally stimulating than modern games - and this fully lives up to those ideals.
The game consists of competing with AI or human-controlled opponents (or not, if that's what you want) to connect trade resources on a map, against the backdrop of a potentially lethal economy and advancing technology. The right scenarios (in the zip I linked to above) will let you go for >150 years - some are even without a time limit - but you typically are presented goals - specific things to achieve by a specific time, in order to get a bronze, silver or gold medal (these goals are usually along the lines of "Connect point x to point y, move twelvety tonnes of cargo K between those two points and amass $------ personal fortune by date z").
I give you fair warning, the graphics aren't going to blow you away, not by a long shot, but the complexity, detail and the intense addictiveness of the game should tickle you if you're prone to being tickled by a game of this type.