How to play I Have No Mouth, and I Must Scream on Mac

I Have No Mouth, and I Must Scream is a point-and-click adventure game based upon Harlan Ellison's short story of the same title. The game's story is set in a world where an evil computer named AM has destroyed all of humanity except for five people, whom he has been keeping alive and torturing for the past 109 years. Each survivor has a fatal flaw in their character, and in an attempt to crush their spirits, AM has constructed a metaphorical adventure for each that preys upon their weaknesses. To succeed in the game, the player must make choices to prove that humans are better than machines, because they have the ability to redeem themselves. Woven into the fabric of the story are ethical dilemmas dealing with issues such as insanity, rape, paranoia and genocide.