Adventure Construction Set: build your own CRPG
Adventure Construction Set is an abandoned application developed by Stuart Smith and published for DOS, Amiga, Apple II and Commodore 64 by Electronic Arts in 1987. As the name suggests, ACS is a game-building system (we're talking about adventure RPGs) that lets you edit maps, items, creatures, etc. Included with ACS is a complete game called Rivers of Light.
Find out more about Adventure Construction Set