The Purple Crystal of the Heavens is a text adventure game that was originally developed using The Adventure Creator on an Acorn Electron, after which graphics were added using The Graphic Adventure Creator on a BBC. The game was later rewritten from scratch for RISC OS computers using Trellis: The Adventure Interpreter, and supplied with it as a demo of its capabilities.
In the game, you take on the role of a new crewman of a pirate ship, cast ashore on a mysterious island in order to find the legendary Purple Crystal of the Heavens.