Wayland has only been stable for clients for little over nine months now, and is now on its second major update since then. The display server that hopes to be more efficient than the ubiquitous xserver used by the vast majority of Linux systems.
Wayland 1.2 has just been released, and now includes a stable server API. As well as this, there’s also updates to the colour management, output scaling has been added, initial Raspberry Pi support has been added and a few advancements in the Wayland Input Method Framework to bring it closer to completion.
You can find out the difference between X and Wayland via a talk Daniel Stone made earlier this year.