Abstract: The principle of operation, basic properties and applications of a new micro-pattern gas detector, Micromegas, will be briefly reviewed. The combination of such precise gaseous detectors with large TPC's is well adapted to low background applications: rare decays, neutrino physics and dark matter detection with recoil direction measurement. Results from the new CERN solar axion search experiment, CAST, will be presented. Special emphasis will be devoted to a new neutrino oscillation proposal, NOSTOS, which will measure low energy neutrinos using a strong tritium source and a spherical gaseous TPC drift chamber. The sensitivity for measuring the mixing angle theta13 and other important parameters of the weak interaction will be presented.