We present the framework of MAESSTRO, which is a software for the Computer-Aided Design of piano soundboards. Based on sound synthesis of piano tones using physical models, it aims at assisting piano makers by providing them the opportunity to predict the mechanical behavior of virtual soundboards and the resulting sounds pf the piano in playing situation. The software is designed so that the synthesized tones reflect faithfully the mechanical and geometrical properties of the soundboard. It uses physical models that numerically simulate the phenomena that are involved in the production of piano sounds, from the impact of the hammer on the string to the radiated sound. We present applications that show the different functionalities of the software, including computing the modal basis of soundboards, studying the driving point admittance along the bridges, and the homogeneity of acoustic features along the tessitura. These applications are helpful to study the mechanical and acoustical impacts of structural modifications of a virtual soundboard.