The Graphic Adventure Creator
Published by Incentive Software, the Graphic Adventure Creator was a game creation system/programming language for adventure games.
Its main advance over the already well-established The Quill was a clever graphics editor, one of very few vector graphics editors for the CPC. This enabled 'rooms' to be portrayed using a minimal amount of memory.
In the heyday of the CPC, few major-label commercial games were produced using GAC (probably fewer than with The Quill), but it had a vast following in the homebrew and public domain scenes - despite a comparatively high retail price of £24.95 (UK).