Here as a user to show my support and appreciation. :) I use Magnum for just about any project involving C++ and graphics. Both the framework and community[0] are fantastic and I'd recommend it to anyone looking for something inbetween Unity and plain OpenGL/DirectX/Vulkan for full control and interoperability with other C/C++ libraries out there like PhysX and ImGui. Go go go!
[0]: https://gitter.im/mosra/magnum