Ravenfield

The real appeal of this game is in the mods. On its own, this game is a super bare bones, basic, vanilla PvE, Red vs Blue FPS with low-res poly graphics, basic levels, short list of simple game modes, and your standard-fare spread of weapons. But there is a whole community of people in the workshop section who have collectively produced THOUSANDS of mods. 99% of them are extremely quick to download and even easier to implement in-game. From things as simple as changing character skins and giving your gun a basic "+" cross hair when hip firing, all the way to flawless recreations of every Titanfall gun, advanced movement mods, map packs recreating levels from your favorite games, and so much more. Gunfire Reborn is another interesting Indie and FPS game.