itch.io

Uses two-dimensional "sprites", 2D images created and used on a flat plane, as opposed to the three-dimensional models or environments found in 3D games.

Things that are available on GitHub

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.

PROCJAM is the Procedural Generation Jam, an annual event about making things that make things.

http://www.procjam.com/

Unity is a game engine for 2D, 3D, AR and more