http://cerea.enpc.fr/polyphemus Polyphemus is a Cyclops in Odyssey whose name roughly means "multiple speeches". It is consistent with the goals of the system, that is, gathering on the same platform: several models: with Gaussian, Eulerian, Lagrangian ... formulations; several scales: from small/local scale to continental scale; multiple polluants: passive, radionuclides, photochemistry, aerosols, ... processing from many inputs (meteorological models, ground data); many advanced methods: data assimilation, ensemble forecasting, models coupling, ... It is written as much as possible with modern computer languages (mainly C++), and only perennial and scalable developments are included. Polyphemus is open. It is open source, distributed under GNU GPL, well documented (for users and developers), and released on a regular basis. Open also means that contributions from other teams are welcome. In this version, Gaussian, Polair3D, Plume-in-Grid models are implemented on the AmpliSIM platform (www.amplisim.com).