GLFW

GLFW is an open-source C library that packs several handy APIs for creating and managing various objects that entail using OpenGL or Vulkan. In addition to surfaces and objects, the library enables developers to handle system specific tasks, including, but not limited to managing inputs from mouse, keyboard, joystick, the clipboard and time local time on the machine.
The primary role of the components is to provide a multi-platform abstraction layer that is useful for programs with the graphic output rendered via Vulkan, OpenGL and OpenGL ES. The platforms where the library can be incorporated include Windows XP and later, Cygwin, FreeBSD, Linux and MacOS 10.8 Mountain Lion and later.
Essentially, the library compensates for the mechanisms that are currently lacking with OpenGL, especially since they stated that their primary concern is to be able to provide rendering into the framebuffer and reading the values stored within. Even though Vulkan packs the aforementioned mechanisms it lacks in terms of surface creation that is platform specific, whereas the API covers the rendering solely.
Nevertheless, the tool cannot be considered a header, extension loader or implementation of the rendering systems. In fact, the aim is to wrap various platform-specific context and surface API and it generally includes the headers that are already provided by the development environment.