In this talk we will review emerging applications of rarefied gas dynamics for microscale sensing, actuation and power generation. Performance of conventional fluidic devices such as pumps, combustors and heat engines decreases at the microscale due to greater viscous and heat transfer losses. Unconventional micro/nanodevices exploit the tight coupling between non-equilibrium gas, liquid and solid-state transport and electromagnetic phenomena to overcome these limitations. We consider three distinct MEMS based on i) very high thermal gradients; ii) increased capillary forces; iii) high electric fields. The first example is Microscale In-Plane Knudsen Radiometeric Actuator (MIKRA) that applies thermostress convection to achieve actuation and control of gas-phase transport by temperature gradients and offers novel methods for gas sensing, pumping, and species separation. In macroscale systems, the operating temperatures necessary to generate significant flow actuation by thermostress convection are prohibitively high. For microdevices, thermal gradients on the order of 107 Kelvin per meter could be achieved, allowing these effects to be exploited. Another examples is Film Evaporation MEMS Tunable Array (FEMTA), a micropropulsion technology that works on microscale effects of surface tension, hydrophobicity, and thin film boiling to create highly tunable thrust using ultra pure water as propellant for attitude control and maneuvering of small satellites and deployable space structures.