2D real-time space exploration / trading / fighting game. The main draw are the space battles. $15 , I raised my definition of cheap just to include this one!
There is an actual storyline with characters and some choices, which you are mostly free to ignore as you colonize planets and earn money from missions. It might be impossible to get through the game as a pure trader with no fighting.
It has been in “alpha” for like 13 years, seems to have a new release every year. It’s very stable, with a large modding community and active discord.
I haven’t actually played since the last patch came out, so my comment is for the version from the start of the year. Colonies were fun and I made a few, but were totally a money sink and vanity project. It felt more comfortable storing stuff and ships there, instead of the safe storage in another system. I don’t think I ever made back all the money I put into them, but there’s more to having fun than money :)