Here are my favorite possibilities. They are all originals except for #1:
1. First Fantasy Campaign’s Blackmoor Dungeon – Original D&D: Go for the gold and glory in the very first dungeon adventure ever created! Travel in the footsteps of the original fantasy roleplayers while spelunking in Dave Arneson’s original Blackmoor dungeon. This game will be based on the original maps and room descriptions generated by Arneson himself. This is where it all started.
2. Mutants of Metal Meet Ratt Punx - Gamma World (First Edition): Your traveling band of mutated metalheads has set up shop in an idyllic island village. One day a mysterious conglomeration of rickety boats bearing a clan of Ratt Punx appears at the harbor. You soon discover that, for unknown reasons, the Punx are systematically getting the local island kids addicted to radioactive cough medicine. Can your band join forces with the angry moms of the island to free the children from the Punx scourge, and to send the children down the righteous metal path?
3. Asteroid Crypts of the Xylbocx Starcult - Classic D&D + Spelljammer: Your group has uncovered a lost text originating from the ancient Xylbocx Starcult. This document contains remarkable instructions for constructing a spacefaring wizardship and for navigating it to a bizarre orbiting asteroid. Can further secrets pertaining to spacefaring and the fate of the starcult be found on - or within - this silent orbiting mass?
4. Horror in the Cloud Mines – Classic D&D: There is a vale, secret and narrow, where trapped and aged clouds live and breath as if they were alive. A century ago these clouds were quietly mined for precious and otherworldly minerals until a mysterious disaster occurred and the vale was sealed by command of the old king. Your party has learned of the location of this vale and senses a chance to achieve extreme wealth. When you enter the cloud mines will you find forgotten deposits of polychromatic cumulonimbical crystals, or will you find madness and death?