Posen, S. JACoW Publishing Geneva, Switzerland Nb₃Sn cavities and other applications for small accelerators, such as for medical application, with a Cryocooler may be one of the major potential applications of SRF in coming years. Axion and dark matter will be another potential use of SRF cavities for fundamental physics. FNAL is also developing small SRF cavities coupled to quantum computer. This lecture will provide some overview of applications SRF¿based.