The MATE project started as a fork of GNOME 2 long back in 2011 following the poor reception of GNOME 3. Since then, it has come a long way and the latest MATE 1.22 releasecontinues to improve the different desktop components.
The biggest change in this release is Wayland-related work. The developers have reworked tons of code to make sure that things work with the Wayland backend. Specifically, it involves a complete revamp of the display applet to control the monitor in a better way.