The libretro project publishes all its sourcecode on Github.
You can view the organization’s body of work here.
Everybody is free to contribute to any of the projects listed here.
Contributions helps the Libretro project and its subprojects to expand and keep getting better.
Lakka and libretro/RetroArch are partners in this endeavor.
You can either donate to RetroArch/libretro or send gifts in order to help it improve.
You can also send hardware donations to particular members that might be interested to provide better integration on certain devices.
You can either donate to Lakka or send gifts in order to help it support more platforms and expand its reach.
View the wishlist here.