OpenQuest

OpenQuest is a short, two-room AGS adventure game, mainly developed with
full documentation to assist newcomers to work towards a professional game.
The aliens Zob and Zif lands on earth to retrieve a powerful relic. They
teleport themselves inside a building where the player, controlling Zob, needs
to solve a few puzzles to retrieve the artifact. The game features only two
screens, about 20 actions and a SCUMM-style interface entirely controlled
through the mouse.

OpenQuest