OpenGL Specifications

Note: OpenGL is not a software, library, and framework, just plain specifications as explained on their website below.  Check the FAQ page https://www.khronos.org/opengl/wiki/FAQ#What_is_OpenGL.3F

OpenGL is the name for the specification that describes the behavior of a rasterization-based rendering system. It defines the API through which a client application can control this system. The OpenGL rendering system is carefully specified to make hardware implementations allowable.

Hardware vendors, the people who make GPUs, are responsible for writing implementations of the OpenGL rendering system. Their implementations, commonly called “drivers”, translate OpenGL API commands into GPU commands. If a particular piece of hardware is unable to implement all of the OpenGL specification via hardware, the hardware vendor must still provide this functionality, typically via a software-based implementation of the features missing from hardware.

GFLW

http://www.glfw.org/

GLFW is an Open Source, multi-platform library for OpenGL, OpenGL ES and Vulkan development on the desktop. It provides a simple API for creating windows, contexts and surfaces, receiving input and events.

GLFW is written in C and has native support for Windows, macOS and many Unix-like systems using the X Window System, such as Linux and FreeBSD.

GLFW is licensed under the zlib/libpng license.