I'm wondering how important that "official" tag is. By "third-party" I mean a product written for a game system, but not by the publisher of that game system.
So Pathfinder products not published by Paizo, D&D products not published by WotC -- and so on. Game systems big and small, as long as the product is not produced by the original game's publisher (whether the original publisher is a big corporation or a one-man-PDF-band).
So Pathfinder products not published by Paizo, D&D products not published by WotC -- and so on. Game systems big and small, as long as the product is not produced by the original game's publisher (whether the original publisher is a big corporation or a one-man-PDF-band).