system
A chat on subreddit /r/wallstreetbets
human
You'd have to break it down into weight classes based on initial cash deposits or make it percentage based leaderboard. I just love the idea of literally turning trading into more of a game than phone apps already have.  
  
 Also just think, you could start making side-bets on the top traders. Gambling on gamblers, ah the possibilities.

gpt
and some weather futures