free implementation of the OpenGL API -- runtime

 Mesa is a 3-D graphics library with an API which is very similar to
 that of OpenGL. To the extent that Mesa utilizes the OpenGL command
 syntax or state machine, it is being used with authorization from
 Silicon Graphics, Inc. However, the author makes no claim that Mesa
 is in any way a compatible replacement for OpenGL or associated with
 Silicon Graphics, Inc.
 .
 This library provides a pure software rasteriser; it does not provide
 a direct rendering-capable library, or one which uses GLX. For that,
 please see libgl1-mesa-glx.
 .
 On Linux, this library is also known as libGL or libGL.so.1.