Fractal-like world generation.
Developed by Binary Systems
Reason for inclusion:
Starflight fit on two floppy disks, yet still managed to contain thousands of star systems, most with several planets each with their own distinctive map and minerals to harvest. It was all done by making canny uses of hashes and fractal map generation schemes. Another game that uses techniques similar to this is Elite, for its map.
Starflight provides many lessons for developers concerning not just generating huge game worlds, but in making those worlds interesting. It uses what I call the "mining" approach to algorithmic content, which is used by roguelikes too: the idea that the randomized areas the player explores are exploited for random wealth, and can be depleted, forcing the player to expand his horizons in order to obtain more.
Here, each individual world tends to be interesting mostly for the minerals it contains. The basic advancement mechanic is to find planets, land on their surface with a scout ship, scan to find stuff to mine, then travel back to base to sell it for better equipment. Some planets have adverse weather effects, some have dangerous wildlife (which can be collected, stored and sold) and some have dangerous conditions on the surface, but there are enough planets with normal atmospheres and no life that players typically don't have to bother with messing around with those if they don't want to.
Advancement loops exist in many different kinds of games, and often don't have a lot of thought put into them. For example, the classic advancement loop used in arcade games is that the player gets better solely through practice. He has no game-sponsored additional powers on level 50 than he had on level 1. Another common loop, which originated in RPGs but has since spread far beyond them, players get better through gaining experience points from defeating monsters and collecting gold from them in order to buy better equipment.
Starflight's loop is financial, for obtaining money is the means of bettering the player's ship. And money is gained primarily through exploring all those thousands of algorithmically-generated planets.
Randomized games (or games that use obscure algorithms to generate their content) frequently use a mining metaphor for their advancement loops. The world is generated automatically by the computer, without much rhyme or reason given to placement of dangers or rewards, and to improve his state the player goes into it to take advantage of what he can. As rewards in the safer areas are depleted, he's forced to travel to more dangerous areas to continue to advance.
Of course, even static exploration games with pre-made areas are like this. The difference is that algorithmically generated game can have much more area, and thus exploration can be a greater portion of the difficulty barrier towards earning a reward than combat or puzzle-solving. Other games that use this general play style, not coincidentally made by some of the same guys, are Starflight II and Star Control II. Star Control II is particularly interesting, for it has a strict time limit that means the player must explore efficiently, and it provides clever clues as to which planets have better resources.
There is a fan-made sequel that's been in the works for some time, Starflight III: Mysteries of the Universe, that has the support of the game's creators.
Star Control II has
a fan-made recreation, titled The Ur-Quan Masters.