I just came across Captain forever, and after playing for a little while, I'm mesmerized, but I'm not entirely sure what I'm supposed to be doing. Do I need to stay in this area, and fight off all comers until I'm destroyed? Do I need to go somewhere?
The goal appeared in readme file is to keep Nemesis(which is your spaceship) from other ships.
The actual 'goal' is to blow up other spaceships and become most powerful spaceship in the Captain Forever space. You'll meet strange X-marked spaceships after get white parts.
EDIT : there's no "ending".
Judging from the "Flight Manual" and some limited time playing the game, the idea is to shoot down other ships and use their pieces to improve your own ship. You start with basic girders, thrusters, and weapons, and upgrade them from winning in firefights.