The GNU C Library project provides the core libraries for the GNU system and GNU/Linux systems, as well as many other systems that use Linux as the kernel. These libraries provide critical APIs including ISO C11, POSIX.1-2008, BSD, OS-specific APIs and more. These APIs include such foundational facilities as open, read, write, malloc, printf, getaddrinfo, dlopen, pthread_create, crypt, login, exit and more.

musl - an implementation of the standard library for Linux-based systems

The cross-platform, open-source build system. Upstream repo: https://gitlab.kitware.com/cmake/cmake

gdb and binutils

Godot Android plugin for the Google Play Billing library

Godot Engine official documentation