Pocket SDR is an open-source GNSS (Global Navigation Satellite System) receiver based on SDR (software defined radio) technology. It consists of a RF front-end device, some utilities for the device and GNSS-SDR APs (application programs) written in Python and C. It supports almost all signals for GPS, GLONASS, Galileo, QZSS, BeiDou, NavIC and SBAS.
From Tomoji Takasu, the author of rtklib.
has a nice table describing GNSS signals.
See also https://s-taka.org/en/awesome-pocketsdr-pocket_trk/
for several blog articles about pocketSDR.