itch.io

Utilizing content created by algorithms rather than human made content. Often utilizes a "seed," a relatively small string that is used to control the randomization algorithm that generates the entire world.

Near infinitely replayable games that usually feature, random generation, perma-death, and brutal difficulty. 

A game in which the player is not constrained to achieving specific goals and has a large degree of freedom to explore, interact with, or modify the game environment