Marleigh Norton came to our prototyping group with a daring concept for a game: no visuals, only audio. Only one button. And it's a conversation game. How?
Every time you press the button, you interrupt the person speaking to you with an interjection. The nature of your interjection varies based on when in the sentence you interrupt. Press the button early in a sentence, and you're likely to blurt out a rude interruption. Press it late, and you might say something more thoughtful.
So how to prototype this? We all came up with our own prototype (divide and conquer!). I figured that it would be easiest to have the player be faced with a ranting character. This way, if the player didn't say anything, the character would just keep on talking. Also, rants are filled with short declarations and rhetorical questions, which provide loads of natural interjection points. For my prototype, the player is conversing with a friend whose marriage is breaking down. Depending on how to player chooses to interject, the friend might be comforted, annoyed, or discover that the player is in fact having an affair with his wife.
Each line of dialogue has several interjection points. If the player chooses to interject, the interjection corresponding to the next interjection point will be read. This will then lead to a different piece of dialogue being spoken in response. This process repeats until the player has ended the conversation, usually by angering or comforting his friend.