  In this paper we present a mobile crowdsourcing platform CrowdCafe, where
people can perform microtasks using their smartphones while they ride a bus,
travel by train, stand in a queue or wait for an appointment. These microtasks
are executed in exchange for rewards provided by local stores, such as coffee,
desserts and bus tickets. We present the concept, the implementation and the
evaluation by conducting a study with 52 participants, having 1108 tasks
completed.
