With the recent discussion around the decision by Ubuntu's management to adopt Wayland, this came to mind again: the version numbers are crazy. (I should run through Linux, next...)

As of November 2010, X11R7.6 is in progress...

This chart compares the releases with the version numbers if you consider, for example, "X11R5" to be "11.5" in decimal, and so on. There are far more important, often subjective, metrics that should be used to weigh decisions, but I present you this: