Alea is an open-source Macintosh application for creating computer games, and in particular graphical adventure games along the lines of Myst, King's Quest and The Secret of Monkey Island.
BoomBot is a developer's framework for writing a bot connecting to the AIM network. It manages the network communication for the bots so that they can be easily written without worrying about AIM itself at all. Bots can be written in Objective-C or Lua.
Lixoo is a extensible, fast and small 2D point'n'click adventure game engine. It features the engine itself and an IDE that let you create full-featured games just by writing the essential code of the game.