A set of specifications for a cross-platform 3D graphics API developed initially by Silicon Graphics Inc. Currently this is primarily used for CAD applications and other professional level 3D design work in Windows NT. Quake has popularized this as a gaming API.

For PC 3D graphics accelerators, there are currently two ways to implement OpenGL support, a full Installable Client Driver (ICD) or a Mini Client Driver (MCD). ICD is the original driver model for OpenGL, and enables vendors to access the entire OpenGL pipeline, allowing them to increase acceleration while maintaining the stability and compatibility of the driver. MCD is a stripped down OpenGL driver, allowing access to only a portion of the OpenGL pipeline, limiting the ability to increase performance and stabilize the driver. MCD is all that is required for games such as Quake.