An extension to provide check-in links and QR codes to CiviCRM event participants, so they can check in with the event's front desk, or even automatically.
When a check-in link is used (e.g. by scanning a QR-code) users with appropriate permissions will be presented with a screen that shows information and allows checking in the participant, thus changing its status (e.g. to "attended"). It also provides an API to allow a remote system to do this.