A cross-platform DirectX replacement.
Created by Loki Games in their efforts to port various MicrosoftWindows games to the Linux world. Though Loki Games have closed/gone into liquidation, their legacy lives on through their excellent library: SimpleDirectMediaLayer or SDL.
SDL was used to port various MicrosoftWindows games to Linux such as Civilization: Call To Power, Descent3 and others. It is OpenSource (LGPL) and now works on many platforms: Windows, Linux, MacOS(X), BeOS ...
The base library plus add-ons provide services such as threads, sound, timers, endian independance, image loading, etc. etc. The library is written in C.
SDL can be found at http://www.libsdl.org/