Mass-interaction physical modeling scheme is often cited as the traditional physical modeling technique, but surprisingly some of the possibilities for musical creation it allows have not yet been pointed out. GENESIS is a graphical environment based on the CORDIS-ANIMA mass-interaction paradigm and designed for musicians. It was conceived so as to help the user "think physical"; that is, to discover and experiment with new ways of creating music, which is necessary when using physical modeling. The paper introduces version 1.5 of the GENESIS environment. Its major features and ergonomic aspects are exposed – especially model representation, low and high level modeling tools, multisensorial simulation facilities. Examples of composer's works are presented.