Starflight was one of the first truly open world video games. It is a space exploration game with role-playing elements. Starflight was initially developed for the PC (DOS) in 1986 but was soon ported to the Commodore 64 (1989), Amiga (1989), Atari ST (1990), and Macintosh (1990). An updated version also appeared on the Genesis several years after the original in 1991.
You as the player play the role of a starship captain exploring the galaxy. You can engage in combat and diplomacy, mine raw materials and perform other tasks. What you do is entirely up to you. As the game progresses, a larger plot becomes apparent involving an evil race of aliens blowing up stars and killing everybody.
As captain of your own starship, you are responsible for maintaining and updating your ship as well as hiring your own crew. You can purchase weapons, armor, shields and of course fuel. Your crew must also be trained to increase their skill which is another thing that costs money.
Starflight has 270 star systems with a total of 800 planets so there is lots to explore. There are also 8 distinctive alien races to deal with or perhaps blow up.
Starflight had a sequel, Starflight 2: Trade Routes of the Cloud Nebula. In addition, Star Control and Star Control II are spiritual successors of sorts with some of the same developers. Starflight is definitely a classic worth playing. I don't think it has been re-released so you will have to track down an original or use emulation. All of the versions are pretty similar with the Genesis version having some minor upgrade.
Screen shots above are from the Commodore 64 version of the game.