A Metafilter user describes notestomary.com, a brilliant game of mysterious, abusive notes from “Robert” to “Mary”:
“A few days ago a post appeared on the Something Awful forums noting a curious website called Notes to Mary. The notes are a series of threatening letters from a high schooler named Robert to his crush, Mary. The goons figured out pretty quickly that they had an ARG on their hands and went to work on solving the puzzle.” … “Robert began interacting with players, sending them strange messages and several series of numbers that appeared to be some sort of code.”
I’m not going to spoil the fun, read the full summary on Metafilter. Hint: the game ended with a popular video meme.