Blit3Dv3
An easy to use cross-platform C++ framework for making 2D (and 3D) games. Supports 32/64 bit, single or multi-threading, gamepads, Angelcode bitmap fonts, and much more. It really shines with how simple it is to make a 2D game using the built-in Sprite class.
Blit3D is under the extremely permissive MIT license. GLFW/GLM/GLEW/stb_image code all under their respective licenses: see copying.txt in appropriate directories (stb_image license is in the file stb_image.h).