JetInBox is a multipurpose program for simulating jets in a cross-flow, sprays and plumes. The fluid can be defined arbitrarily, e.g.air or water. Mass and momentum entrained in the jet are integrated by ordinary differential equations over time. Transient 3D solutions are obtained within a few seconds. An arbitrary number of jets can be defined by entering the injector positions and injecting velocity vectors. JetInBox can be applied widely by selecting different cross-flow types, addressing integral plug flows and various swirl profiles. Gravitational forces can be taken into account for instance when modelling water sprinkler systems for irrigation or fire protection purposes. 3D representations and animations of the JetInBox solution can be viewed from different angles. Transient solutions can be exported to text files.