Top Secret: Meta Agents is on its way to becoming a reality.
I've been proposing this for almost a year now and have now managed to wrangle up a number of players.
The idea is to play a Play by Post game of TSR's 1980 RPG "Top Secret" using snail mail. Players play sleeper agents that have been using their real identity as a cover. Mission packages and agents reports are sent back and forth creating the story.
"Too secret for WikiLeaks, too dangerous for the Internet"