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.

Godot Engine - The free and open source 2D and 3D game engine

Pretty sure everything is indie on itch.io but just in case you want something extra indie.

Featuring aesthetics, gameplay, or themes reminiscent of classic video games. Often characterized by pixel art, chiptune music, or mechanics popularized in earlier gaming eras.