XFree86 4.3.0 is the sixth full release in the XFree86 4.x series.
XFree86 4.x is the current XFree86 release series. The first release in this series was in early 2000. The core of XFree86 4.x is a modular X server. The 4.3.0 version is a new release that includes additional hardware support, functional enhancements and bug fixes. Specific release enhancements can be viewed in the Release Notes.
Most modern PC video hardware is supported in XFree86 4.3.0, and most PC video hardware that isn't supported explicitly can be used with the "vesa" driver. The Driver Status document has a summary of what hardware is supported in 4.3.0 compared with the old 3.3.x (3.3.6) series. It is a good idea to check there before upgrading if you are currently running 3.3.6 with older hardware.
XFree86 is produced by The XFree86 Project, Inc, which is a group of mostly volunteer independent developers. XFree86 is a non-commercial organisation, and would not be viable without the invaluable development contributions of volunteers. This release is dedicated to all who have supported and contributed to XFree86 over the last eleven years.