Spectroscopy is a powerful analytical technique aimed at identifying molecular systems in a laboratory sample. Among the different spectroscopies, Raman scattering is particularly suitable for analytical detection, due to its sensitivity to molecular structure. Unfortunately, conventional Raman scattering suffers from a relatively low-in-intensity signal, which can however be hugely enhanced if the molecular probe is adsorbed on noble-metal nanosubstrates. The resulting technique, named Surface-Enhanced Raman Scattering (SERS), allows single-molecule detection with non-invasive approaches, and can be effectively exploited in many fields, including biosensing. The actual interpretation of SERS signals in terms of molecular patterns benefits from the coupling with theory and simulation. The goal of GEMS is to provide the scientific community with a user-friendly platform that can guide the interpretation of experimental results and predict molecular and supra-molecular signals that have never been measured.