Wayland
The next iteration to X, the traditional Unix display server. Wayland, similar to X, is an entirely new protocol leaving to other tools to implement desktop systems. Thus, it needs a new ecosystem of programs to run inside of a Wayland-based desktop sessions.
Ecosystem
Sway is a compositor and a window manager serving as a drop-in replacement for i3.
wlroots is an unopinionated modular compositor library.
Wayland book is a free book showing the basic ropes of working with Wayland-based systems.
XWayland is an implementation of X display server to accept Wayland input.
xdg-desktop-portal-wlr is a portal backend for wlroots.
GNOME Shell and KDE Plasma is slowly supporting Wayland.
Application support
While Wayland support for various legacy systems are increasing recently, one still have to be cautious with support.
Several graphical toolkits support Wayland.
Starting at version 27, OBS Studio supports Wayland-based systems.
wlrobs is a OBS Studio plugin supporting wlroots-based compositors.
Grim is a command-line tool for getting screenshots.
wf-recorder for recording with wlroots-based compositors.