As they are useful and convenient, rainfall-runoff models are widely used in research and engineering. Applications of rainfall-runoff models range from flood risks estimation, to water resources management and low-flow related issues. The Catchment Hydrology Group at INRAE (Antony, France) has developed a set of conceptual GR models over the past 30 years with the main objective of designing models that are as efficient as possible in terms of streamflow simulation, and are applicable to a wide range of catchments with low data requirements. In recent years, in order to provide access to these hydrological models, INRAE has developed an open-source package named airGR for the R free software environment. This tool embeds the GR4H, GR4J, GR2M and GR1A models, among others, which operate at the hourly, daily, monthly and annual time steps. This package also includes a snow accumulation and melt module, a calibration tool, efficiency criterion calculations and plotting facilities. Recently, a galaxy of tools has formed around airGR (hydroGR.github.io/airGR). The airGRteaching R package is designed for simple applications and requires limited coding knowledge. It also offers a graphical user interface particularly useful for educational purposes. The airGRiwrm R package (for integrated water resources management) provides tools to integrate human influences in a semi-distributed hydrological model, namely local flow injections or withdrawals based on predefined flows, or on user-defined decision algorithms given model outputs during simulation. The airGRdatassim R package allows assimilating uncertain observed data to constrain the GR model predictions. Two data assimilation methods are available: the ensemble Kalman Filter & the Particle Filter. It also includes a model inputs perturbation function to generate probabilistic meteorological forcings. In addition to these R packages, the airGR constellation includes two web applications available on sunshine.irstea.fr/. First, the airGRteaching GUI is a demo of the tool embedded in the R package. Second, the airGRmaps GUI provides regionalized parameters for GR daily hydrological models from geographical coordinates or by browsing on the map, over France.