Hargrave also produced four Arduin Dungeon Modules and several fantasy item collections, which were published by Grimoire Games.

[3] Hargrave's work was perhaps the first "cross-genre" venture into fantasy RPG, and it included everything from interstellar wars to horror and historical drama.

Arduin was in fact one of the earliest challengers to TSR's Dungeons & Dragons, and a leading representative of the high-entropy, multiversal campaigns then prevalent in RPG circles of the era.

[4]) Hargrave also frequently contributed to various magazines such as Different Worlds, Alarums and Excursions, and Abyss.

Around 1979, Hargrave operated a game store in Concord, California, called Multiversal Trading Company.