The source code is hosted in Github.
Most of the projects will have an open source license, like:
Bear in mind that some projects will have a different open source license, so check the project description page for more details about the license or contact the creators of the project.
All the generated data by the volunteers are, unless otherwise stated, under the Open Data Commons License. Check the description the project's page for further details about which license is going to be applied.
All the General Content of the page is under a Creative Commons License BY-SA 3.0 Unported.