The ground-based GPS approach of the atmospheric sounding has demonstrated its efficiency for deriving atmospheric parameters with high quality and spatiotemporal resolution. Its potential for various applications in weather forecast and climate research is nowadays worldwide recognized by atmospheric scientists. During the last decade, the realization of near real-time data retrieval in dense ground-based GPS networks has become a well-established atmospheric observing system. The number of national weather services which use GPS-derived atmosphere products in their day-by-day operational forecasts increases constantly. Programmes like E-GVAP (the EUMETNET EIG GPS Water Vapour Programme, egvap.dmi.dk) which coordinates the efforts of meteorological and geodetic research for improving weather forecasts in Europe are very successful and promote further cooperation. The main methodological focus of the GFZ activities in GNSS atmosphere sounding is the improvement of the observation technique. Currently, this comprises investigations related to real-time data analysis and to transition from single GPS to multi-GNSS including Galileo, GLONASS and BeiDou. More than 90 GNSS satellites are already available and about 120 will be in the near future. When Galileo and BeiDou will become fully operational up to 40 satellites may be observed continuously at any station. This will lead to a significantly increased spatiotemporal resolution of the atmospheric measurements, compared to GPS alone. The main focus of the current scientific GFZ activities is the development of advanced multi-GNSS tropospheric products. We introduce recent results of these developments and present examples of their applications in atmosphere monitoring.