OpeNoise is a multi-platform, public and open-source noise assessment project, implemented by the Environmental Protection Agency of Piedmont Region (Arpa Piemonte - Italy), with the support of the Municipality of Turin and the Province of Turin. The goal is to provide a first-level and free access tool for public administrations, consultants, universities and companies in the field of environmental acoustics. The OpeNoise project is divided in three branches: an application for noise measurements through mobile devices, a tool for acoustic data analysis, developed in the R-Project framework for statistical computing, and a script for noise mapping, available within the free and open-source geographical system Q-GIS. This paper describes the major technical features of these tools, their possible practical uses, as well as some application examples and planned future developments.