Aleph One Bungie's Now Data Free First Person Reaction To Doom

Aleph One, available for Linux, Windows, and Mac OS X, is the open source continuation of Bungie's Marathon 2 game engine, enhancing Bungie's original Marathon games with modern OpenGL shader support, Internet co-op and multiplayer, modern mouse-look and gamepad support and plugin support for modifications. It supports Marathon through a fan-made conversion, Marathon 2 and Marathon Infinity natively, all three games can be download for free. There are many third party scenarios and net maps also available.

Simple DirectMedia Layer Multi Platform Core Engine

Simple DirectMedia Layer (SDL) is a cross-platform development library designed to provide low level access to audio, keyboard, mouse, joystick, and graphics hardware via OpenGL and Direct3D. It is used by video playback software, emulators, and popular games including Valve's award winning catalog and many Humble Bundle games. Supports officially Windows, Mac OS X, Linux, iOS, and Android. Support for other platforms may be found in the source code. Is written in C, works natively with C++, and there are bindings available for several other languages, including C# and Python. SDL 2.0 is distributed under the zlib license. This license allows you to use SDL freely in any software.