If you are looking for the latest release version of the library, you can download a tarball for Windows or Linux/macOS here.
The Open Navigation Surface is free software provided under the BSD license.
There are no restrictions on use or adaptation of the source code, although we would prefer if you contributed modifications, extensions and bug-fixes back to the project rather than releasing a (potentially incompatible) version of your own. The software comes with no warranty, express or implied, as to fitness for any purpose. That is, the code is provided for your convenience, and you agree by downloading the code distribution that the Open Navigation Surface Working Group and its members are not responsible for any loss or damage, of whatever kind, that may be caused to you by the use of this software, or by you because of your use of this software.
If you prefer to get access to the latest source code, you can obtain it by cloning the repository, which you can find here. You should clone with:
git clone https://github.com/OpenNavigationSurface/BAG.git