Oolite is kind of a tribute to the legendary DOS game, Elite. Personally, I think Oolite is better. The flexibility of the game is flat out amazing. The game is fueled by the players themselves making additions to the core part in what are called Expansion Packs. Last I checked there were nearly 800 expansion packs available. Some are as simple as adding a spiffy paint job to an existing ship, others alter the way the whole gameworld functions. Fortunately, they are well described so you know what you are getting into. There is a good wiki and the community is active and as far as I can tell, pretty friendly.
If you liked the original Elite, or Elite: Dangerous, you will dig this.
My only complaint about the game is that, for me at least, it causes some kind of highly localized warping of the fabric of time-space, getting me in trouble with my Darlin' Gal for playing "for hours on end" when I know I just started a few minutes ago.
Try it, you'll like it. It is absolutely free, no ads, no b.s.