Redline is the name of a proprietary Windows application programming interface for video cards made by Rendition. The original DOS version of the API was named Speedy3D. The company was bought out by Micron as the consumer market settled around NVIDIA and ATI Technologies as the dominant graphics card suppliers. Rendition's hardware, and associated API, are no longer in the retail market.
References
Redline (API) Wikipedia(Text) CC BY-SA