Global Navigation Satellite Systems receiver defined by software. It performs all the signal processing from raw signal samples up to the computation of the Position-Velocity-Time solution, including code and phase observables. It is able to work with raw data files or, if there is computational power enough, in real time with suitable radiofrequency front-ends. This software is mainly developed at CTTC (Centre Tecnologic de Telecomunicacions de Catalunya, http://www.cttc.es) with contributions from around the world. More info at https://gnss-sdr.org