Windowing concept abstraction library for X11 and Wayland

Libxfce4windowing is an abstraction library that attempts to present windowing concepts (screens, toplevel windows, workspaces, etc.) in a windowing-system-independent manner. Currently, X11 is fully supported, via libwnck. Wayland is partially supported, through various Wayland protocol extensions. However, the full range of operations available on X11 is not available on Wayland, due to missing features in these protocol extensions.