data.gouv.fr is the open platform for French public data, run by Etalab within DINUM. It both hosts datasets and references those published elsewhere, covering administrative boundaries, the national address base (Base Adresse Nationale), transport, environment, and a wide range of local government data.
Released largely under the Licence Ouverte, the data is free to reuse including commercially. For precise cartographic base layers and reference geographies, data.gouv.fr is complemented by IGN's Géoservices platform.