This article introduces the software Melange, a 3D lattice-particle hybrid model. The software was specifically designed in order to simulate ductile visco-elasto-plastic deformation and can be used to study tectonic processes in the lithosphere from the micro to the macro scale. Melange is under an open source license. The code takes both relevant yield mechanisms for the deformation of lithospheric material into account: dynamic brittle failure and ductile creep, where ductile creep is modeled as viscoelasticity. The software considers effects of the local geology, of the inherent disorder of geomaterials, of rheological layering of the lithosphere and applies repulsion when the material fractures. Driving forces are the externally applied strain and the gravitational load. Melange applies an elastically isotropic regular 3D lattice with HCP geometry and next-nearest neighbor interactions. Young's modulus, viscosity, material density and system size can be freely chosen. Poisson's ratio is restricted to values <0.25. The most important innovation of the software is a physically consistent scheme to model viscoelasticity in a lattice-particle model. The scheme couples the local lattice-geometry to the time-dependent volume-conservative viscoelastic deformation of particles. The procedure achieves the typical viscoelastic stress-strain relationship. The article incorporates a number of benchmark simulations, where the model output is being tested and evaluated. The results obtained with Melange show strong similarities with the benchmark values, e.g., stress fields in crack vicinity. Geologically relevant examples include structures associated with the brittle-ductile transition, growth of wing cracks and brittle graben formation.