One of the earliest and most famous examples is Elite [2]:
> The Elite universe contains eight galaxies, each with 256 planets to explore. Due to the limited capabilities of 8-bit computers, these worlds are procedurally generated. A single seed number is run through a fixed algorithm the appropriate number of times and creates a sequence of numbers determining each planet's complete composition (position in the galaxy, prices of commodities, and name and local details; text strings are chosen numerically from a lookup table and assembled to produce unique descriptions, such as a planet with "carnivorous arts graduates").
For more details and screenshots see this great blog post: https://evoniuk.github.io/posts/pitfall.html
The proc gen is also consistent and persistent, based on some initial seed value decided upon at some point in the game's genesis; A CMDR who jumps their ship to some star system never visited before has that star system generated by their game client according to its algorithm - all the system bodies and their types and classes and whatever's on any planets, if anything.
Another CMDR who subsequently visits it will see the same thing the original CMDR saw.
It's a thing of beauty.
I am not joking when i say that E:D is in my top 3 games of all time.