Doppelganger Dungeon

From the introduction:

Doppelganger Dungeon is not quite a retroclone, but rather a doppelganger
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Doppelganger Dungeon, thematically, is meant to fit somewhere between certain famous Little Brown Books, their subsequent supplements, and a Blue Book of renown. The works of the Judges Guild from this same era of publication were inspirational and formative for this author. Conceptually therefore, an era of dungeon focused adventure informs this author’s writing. The scope of the game strictly confines itself to Dungeon Adventures, with supporting Wilderness.