Allegro!

Vulkan is the result of 18 months in an intense collaboration between leading hardware, game engine and platform vendors, built on significant contributions from multiple Khronos members. Vulkan is designed for portability across multiple platforms with desktop and mobile GPU architectures. Vulkan is available on multiple versions of Microsoft Windows from Windows 7 to Windows 10, and has been adopted as a native rendering and compute API by platforms including Linux, SteamOS, Tizen and Android.

Microsoft DirectX is a collection of application programming interfaces (APIs) for handling tasks related to multimedia, especially game programming and video, on Microsoft platforms.

WebGL is a cross-platform, royalty-free web standard for a low-level 3D graphics API based on OpenGL ES 2.0, exposed through the HTML5 Canvas element as Document Object Model interfaces. Developers familiar with OpenGL ES 2.0 will recognize WebGL as a Shader-based API using GLSL, with constructs that are semantically similar to those of the underlying OpenGL ES 2.0 API. It stays very close to the OpenGL ES 2.0 specification, with some concessions made for what developers expect out of memory-managed languages such as JavaScript. »

Libgdx is a Java game development framework that provides a unified API that works across all supported platforms.

Pygame is a set of Python modules designed for writing games. Pygame adds functionality on top of the excellent SDL library.

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.

SFML (Simple and Fast Multimedia Library) is a portable and easy-to-use API for multimedia programming. It is written in C++ with bindings available for C, D, Python, Ruby, OCaml, .Net and Go. It can be thought of as an object oriented alternative to SDL.

Cross-platform windowing and multimedia library for Python.

A platform independent 2d game programming framework for c/c++ programmers with least possible dependencies for easy porting and with focus on easy API calls and the requirement of commercial programmers.

Arianne is a multiplayer online games framework and engine to develop turn based and real time games. It provides a simple way of creating games on a portable and robust server architecture. The server is coded in Java and you may use Python for your game description, provides a MySQL or H2 database backend and uses an TCP transport channel to communicate with hundreds of players.

HGE is an easy to use yet powerful hardware accelerated 2D game engine. It is a full featured middleware for all who want to develop commercial quality 2D games rapidly and easily. It covers all imaginable 2D game genres: you could create everything from a simple puzzle to advanced multilayered platformer or strategy without even thinking of any non game logic code! And you don't have to know anything about "window messages", DirectX programming and all that stuff. Instead you can start developing your own game within 15 minutes! »

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).