Avalanches, debris flows and rockfalls are gravitationally driven natural hazards. Hazard mitigation experts are confronted with the problem of predicting the trajectories, runout distances and velocities of such fast moving processes in mountain terrain. Numerical simulation is difficult because the dynamical behaviour of each process is governed by different flows and impact mechanics in interaction with terrain features. Here we report on the development of a software package which is intended to assist practitioners and researchers to simulate these gravitationally-driven natural hazards within one single software environment. The software includes four different process modules to predict (1) snow avalanches, (2) debris flows, (3) hillslope debris flows and (4) falling rocks. The process modules are linked together by a common user interface that simplifies the specification of the three-dimensional mountain terrain model, detailing the starting conditions and the model parameters. The tool facilitates a direct comparison of the influence of mitigation measures on several different processes (e.g. the influence of avalanche retention dams on avalanche runout as well as debris flow runout and rockfall). The tool interactively displays the results of the process intensity to support the generation of hazard intensity maps and the influence of mitigation structures on changes in intensity.