The schematic and 3D libraries supported by KiCad team.
The footprint libraries are the *.pretty repos themselves and are used online by default. If you want to download them locally, the library-repos-install.bat and library-repos-install.sh scripts in the KiCad source can do this automatically.
For more information, please check: http://kicad-pcb.org/contribute/librarians/
Please, check the CONTRIBUTING.md file.