Since I seem to be writing game reviews, well, here's an oldie but goodie from the Mac shareware side (the final game in the series was dual-platform).
The original 1996 game was the solo creation of Matt Burch, who programmed, wrote, created the content, etc. It wasn't the simplest game to mod, requiring editing resource forks among other things, but even before third-party editors came out people were writing mods. The mod community is still going strong, with some of their efforts more extensive than the shipped game (and in the case of Escape Velocity Nova, Ambrosia Software hired the mod team and they were the primary content creator.)
The game is a hybrid open world game; trading, role playing, combat. You play a single pilot, represented on-screen (in a 2D star map) by the ship you are currently flying. The trading takes place between different worlds, where you can either chose to accept cargo missions being offered to you (which have a higher return) or purchase bulk commodities yourself and try to find a market elsewhere. Very early Andre Norton in feel, there.
Pirates and other hostiles may attack you en-route (plus, some systems are being hotly contested by the various political factions and you can get caught in the crossfire.) Which brings in the combat; you can chose to arm your ship and defend yourself, which extends right up through taking bounty hunter missions to becoming a pirate yourself.
And, lastly, there are the major threads. These operate via the same mechanics; jumping from system to system, landing on worlds and getting the landing blurb, interacting in shipyards and bars (aka, you click on the "visit bar" button and you may get a dialog pop-up, with a fairly primitive dialog tree), taking cargo, and of course fighting.
What makes the major threads different is that they present a developing story, and the scripting allows the world to change in response. You can agree to smuggle a few parts for the Rebellion, you get access to world that you couldn't land at (or perhaps, that didn't even appear on the map), abilities to purchase new ships, and eventually you are sent out to take part in massive fleet engagements. The traffic around key worlds, the description when you land, even the image of the world in the map, can all change as the story develops.
Because of the open-ended nature of the world, you can of course game this a little. In Escape Velocity Nova, one of my usual methods with a new character was to find my way to this little Irish world full of mercenaries and Guinness and in need of medical supplies. Which meant a relatively safe four-jump bulk cargo route between them and Sol was profitable to almost 200% of trip costs.
So I'd run bulk cargo until I could afford to start hiring more hulls, run that until I could upgrade my own ship, hire more hulls again, geometrically progressing until (if I hadn't gotten bored already) flying back and forth with six Leviathan freighters.
At which point you have the cash to make a really good pirate-stomper. I'd then go lurk in the nastiest systems smashing and boarding pirates (and, with a lot of luck, capturing their vessels to add to my new fleet of combat vessels). And running up my "combat rating." Because many of the important plot hooks will not be offered to you until you've got a decent reputation as a fighter.
And, yes, unloading eight Auroran-built railguns that you've strapped all over the hull of a converted freighter at some poor pirate Manticore will get you that rep nice and fast.
Nova, the last remake, improved the graphics and other options in a number of ways. The ships (and other 2D map objects) are represented by sprites; pre-rendered top-down images of the ship, one for each facing you can take. Nova improved this by adding alternate sprites for banking, engines on and off, weapons live, and simple animations. Nova also added custom HUDs for each ship, and the ability to customize the landing screen quite a bit.
Unfortunately, the ATMOS group also wrote their six core scenarios (the major world-changing plot threads) in a way that is often ridiculous, rather railroading, and basically takes play out of the player's hands. You get told what you did as often as you get to actually do it, and what you told is often hard to reconcile with your mental image of your character. This is not helped at all by the fact that over half of the scenarios have some sort of messiah complex built in. You become a virtual god in at least one.
Fortunately, there are extensive mods, called either "plug ins" (for smaller ones that fit within an existing game) and "Total Conversion" plugs that remake the entire game. One -- which I've unfortunately forgotten the name of -- presented a poetically realized story of lost memory and rekindled purpose. And had some clever and unique game mechanics as well.