You could almost call Orbital Trader a casual game for geeks. It's a space trading game--you start with a small starship, move from one planet to another buying and selling stuff. You're limited to a single star system (no FTL here), and planets move over time, and you're restricted to transfer orbits, so closer planets are a lot easier to get to. Each planet has only a single commodity, and it's easy to find destinations where you can make a profit (mouseover your planet, and you'll see what its commodity fetches everywhere else in the system). And that's--really about all there is to it.
Well, yes, you can upgrade your ship over time; and as time goes on, you can invest in upgrades to the planets, building 'structures' which improve their productivity, demand, and so on. There's fairly a deep tech tree, in fact.
Except that--there are no competing AIs, and no victory condition (though there is a high-score list). So what you're doing is amassing the highest profit value you can.
It's a fun little game to fire up and play for a half-hour or so and see if you can make more money than you did the last time--and it's not unattractively done, for a little 2D shareware game, albeit the lack of sound is missed.