The best Game Development alternative to OpenGL is Amethyst Game Engine, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 10 alternatives to OpenGL and four of them are Game Development Tools so hopefully you can find a suitable replacement. Other interesting Game Development Tool alternatives to OpenGL are Crystal Space, Allegro and Mantle.
Amethyst uses gfx-rs to render graphics with Vulkan or Metal. It is meant to be used for 2D and 3D, with various utilities for both types of games. It should be beginner friendly but also allow more advanced uses such as custom render passes and GLSL shaders.
Crystal Space is a mature, full-featured Software Development Kit (SDK) providing real-time 3D graphics for applications such as games and virtual reality. It is free (LGPL) and cross-platform (Windows, GNU/Linux, Mac OS X).
Allegro 4 and Allegro 5 are cross-platform, libraries mainly aimed at video game and multimedia programming. They handle common, low-level tasks such as creating windows, accepting user input, loading data, drawing images, playing sounds, etc.
Mantle is a graphics API specification; the software component that makes it easy to apply programming techniques and optimizations written for consoles to PCs with Graphics Core Next (GCN) Architecture.
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Crystal Space is a software using 3D rendering/drawing APIs. OpenGL is a rendering/drawing API.