PerplexCity was great - an ARG that gave away $500,000 if you found the prize. They paid for that by selling game cards (difficulty: 30min crossword to a proof

PerplexCity was great - an ARG that gave away $500,000 if you found the prize. They paid for that by selling game cards (difficulty: 30min crossword to a proof of the Riemann Hypothesis). However, the VC-backed company didn't deliver the second wave as promised and now does something else. It was one of the first serious attempts to commerciaise ARGs.