X11R6.9 is the ninth and final full release in the X11R6 series, and X11R7.0 is the first release in the new X11R7 series.
The 6.9 version is a new release that includes additional hardware support, functional enhancements and bug fixes. The 7.0 version is built from the same source code as the 6.9 so it contains the same additional hardware support, functional enhancements and bug fixes; however, it has been split into logical modules that can be developed, built and maintained separately, but still fit together coherently into the larger source code base as they have in the 6.9 tree. Specific release enhancements can be viewed in the Release Notes.
X11R6.9 and X11R7.0 are being released at the same time to assist in the transition from the older monolithic source tree to the new modular source tree. It will take time for everyone to make this transition, so we will maintain the older X11R6 series through update releases to both X11R6.9 and X11R6.8.
Most modern PC video hardware is supported in both releases, and most PC video hardware that isn't supported explicitly can be used with the "vesa" driver. The Release Notes has a table showing the drivers provided with X11R6.9 and X11R7.0, and links to related documentation.
The X.Org Foundation X releases are produced by the X.Org Foundation. The X.Org Foundation has been formed as a Delaware corporation organized to operate as a scientific charity under IRS code 501(c)(3) chartered to develop and execute effective strategies which provide world-wide stewardship of the X Window System technology and standards. Membership in the X.Org Foundation is free to all participants. Applications for Membership are now being accepted, and active participants in the further development of the X Window Technology are invited to complete a membership application. The X11R6.9 and X11R7.0 codebase forms the fourth X Window System release since the formation of the X.Org Foundation and includes code from the X Consortium, the Open Group and the XFree86[tm] project. This release is dedicated to the greater X community, developers and users alike.