The Goblin Laws of Gaming is a homebrew rules-light tabletop adventure game in the vein of AD&D, heavily annotated and expanded by a variety of clever goblins across the internet. Here's the link to Arnold K's original rules. Almost all GLOG content is broadly compatible, and there's hundreds of thousands of words of classes and backgrounds and systems and even a few adventures out there for GMs and players to mix and match to their hearts' content, all for free!
If you're looking for a change of pace from the mass of 5e or 3.PF games dominating the fantasy RPG landscape, I highly recommend it! It's powerful, lethal, easy to learn, and quick to set up.
I've written three different hacks of the Goblin Laws of Gaming: Mimics & Miscreants, SAWN-OFF, and most recently GOOSEFLESH; each linked in the image of their cover below.