The XFree86 Project was founded to freely maintain X servers and critical clients for "IA-32" systems. Their work has since expanded to support other non-Intel architectures, but the purpose continues.
"The XFree86 Project, Inc is a non-profit corporation of the state of Texas, USA. The primary charter is to design, implement, and distribute, as free software, an implementation of the X Window System. The software implements the X Window System specifications for many Unix and Unix-like operating systems. All products of The XFree86 Project, Inc, are freely available, and freely redistributable. "
Tuning tips on how to make X run faster without changing hardware. But as it dates back to 1998, a lot of it is pretty obsolete.
The direct rendering infrastructure, also known as the DRI, is a framework for allowing direct access to graphics hardware in a safe and efficient manner. It includes changes to the X server, to several client libraries, and to the kernel. The first major use for the DRI is to create fast OpenGL implementations.
The X Damage Extension allows applications to track modified regions of drawables.
The X server project holds sources to build an X server separately from a full X distribution. The only drivers supplied are based on the kdrive framework.