We propose GadJets, an approach to remotely actuating passive materials and mechanisms using air jets for interactive and shape-changing tangible user interfaces (TUIs). Compared to previous HCI research in remote actuation, air jets offer relatively strong, distant, and safe actuation with simple control. Leveraging these advantages, we can selectively actuate multiple passive materials and mechanisms (or GadJet modules) using only one actuator. We defined a design space to outline the basic architecture and generalizable primitives for air-jet-based TUIs. Also, we exemplified our approach with diverse GadJets modules and proof-of-concept implementation of a computer-controlled air jet system. Finally, we developed a visualization system of the estimated air range based on pre-collected data to support user control. With the vision of deploying multiple passive GadJet modules in an environment fused with the actuated air jets, we demonstrated applications of interactive tabletop objects, an actuated workbench, and an actuated shelf.