Wikipedia
OpenSeaMap
OpenSeaMap is a software project collecting freely usable nautical information and geospatial data to create a worldwide nautical chart. This chart is available on the OpenSeaMap website, and can also be downloaded for use as an electronic chart for offline applications.
The project is part of OpenStreetMap. OpenSeaMap uses the same database, and complements the spatial data with nautical information. Such data may be used in accordance with the Open Database License. This ensures integration into printed materials, websites and applications is possible, without being limited by restrictive licenses, or having to pay fees. The naming of OpenSeaMap as a data source is required for data sharing.