These are the official extensions directly bundled with Game Develop.
First, take a look at the Readme.md at the root of the repository and the developer documentation. Extensions always contains an Extension.cpp and/or a JsExtension.cpp file that are used to expose the extension to Game Develop IDE.
After being compiled, extensions binaries are put in Binaries/Output/Release_{OS}/CppPlatform/Extensions (or Binaries/Output/Release_{OS}/JsPlatform/Extensions), where {OS} can be Windows, Linux for example.
Any contribution is welcome! Whether you want to submit a bug report, a feature request or any pull request so as to add a nice feature, do not hesitate to get in touch.
Extensions are provided under the zlib/libpng License. See the notice at the top of each source file of an extension for any particular information. External libraries can be used by extensions (Box2D, Dlib or SPARK for example). See their licenses in their directories.