A multi-physics solver for nuclear reactor analysis, named GeN-Foam (Generalized Nuclear Foam), has been developed by the Laboratory for Reactor Physics and System Behavior at the EPFL and at the Paul Scherrer Institut (Switzerland). The developed solver couples: a multigroup neutron diffusion or SP3 subsolver; a thermal-hydraulics sub-solver based on the standard k-epsilon turbulence model, but extended to coarse-mesh applications through the use of a porous medium approach for user-selected cell zones; a displacement-based thermal-mechanics subsolver to evaluate thermal deformations of structures; and a finite-difference subscale fuel model that can be used in coarse-mesh simulations of the core to evaluate the local temperature profile in fuel and cladding. A first-order implicit Euler scheme with an adaptive time step is used for time integration, and the coupling between equations is semi-implicit, using the Picard iteration. Three different meshes are used for thermal-hydraulics, thermal-mechanics and neutron diffusion, and fields are projected between different meshes through a standard volume-averaging technique. GeN-Foam features a general applicability to pin- or plate-fuel, or homogeneous nuclear reactors. Its application in several cases of interest has shown stable numerical behavior, the possibility of obtaining reliable results for traditional reactor types, as well as the possibility of investigating non-conventional reactors, whose analysis cannot be easily carried out using nuclear legacy codes.