The aim of this paper is to introduce Mimosa: a generic platform for modelling and simulation and to show its applicability to the specification of multi-agent simulations based on the AGR (Agent-Group-Role) model. The Mimosa platform allows to describe the appropriate formalisms for the targeted models and then the models themselves. Moreover, it is able to articulate several models for modelling complex systems. This capability is illustrated by showing how the notions of environment, agents, groups and roles are specified, instantiated into concrete models and then run through the specification of the notion of scheduler. Finally, an running example is given.