Players compete in auctions to purchase different cards representing the districts of Chicago. The innovative bid mechanism is that players may not bid a number whose 'ones' digit matches the number on any card they have previously won. The innovative payout mechanic is that players owning a card whose number matches the 'ones' digit of a bid stand to gain a share of that bid.Asmodee Editions' Serengeti uses a different theme, instead of purchasing districts of Chicago, each players purchase African art with the local currency 'Hongo'. - BoardGameGeek