Passbook enabled apps have begun making their way to the App Store, with major corporations like Major League Baseball, Ticketmaster, Fandango and Lufthansa offering event and flight tickets via Passbook, and Walgreens offering access to its rewards program via the service.
The Next Web has details on how Passbook works:
The passes are issued by companies directly to customers via email or apps or any other avenue that they choose and are added to a user’s Passbook automatically. There is no app required for use besides Passbook itself, though companies can choose to include ‘pass update’ functionality in their apps for those that want to make changes after the fact.
The search engine on our sister-site AppShopper is keeping track of Passbook-enabled apps as they get released.