Quilboar was an RPF forumer that presumably popularized the "Free-Choice" form of roleplay, which is vaguely similar to D&D, but is basically a multiplayer ISRP. "Free-Choice" are roleplays where players post what they decide to do, and wait for the GM (owner) to tell them the result of their decisions, and what happens next. The players would then make another action, and so forth. It is called "Free-Choice" because there are little to no limits on the choices the players can make. (i.e. it is not a game where you must pick "A, B, or C")
The first of Quilboar's roleplays to become popular was called Tyrant's Pawns, which was mission-based and set in a military sci-fi setting. Later popular roleplays he made were more open-world; he made Essence (medieval fantasy-based), Dominion (dystopian future-based), and Overcast (zombie-based). Dominion and Overcast had 110 and 140 pages, respectively. Additionally, he created numerous mini-RPs, sometimes related to the larger universes.
Quilboar owned a medieval fantasy-based clan called The Thismonian Kingdom which eventually got over 1000 members, but eventually he lost interest and totally wrecked it.
He now mostly roleplays on Garry's Mod and RPN.