The X.Org project provides an open source implementation of the X Window System. The development work is being done in conjunction with the freedesktop.org community. The X.Org Foundation is the educational non-profit corporation whose Board serves this effort, and whose Members lead this work.
The last full release of the entire X.Org stack was X11R7.7 - since then individual X.Org modules have been released independently as needed - see the xorg-announce archives for details of those releases, and https://www.x.org/releases/individual/ for downloads. Information about all releases is available.
A visual guide to how X11 and Wayland work.
Video to help you better understand what X11 and Wayland