X11GTK

X11GTK is a software layer that integrates the GTK toolkit with the X Window System (X11) to enable GTK-based applications to render within X11 windows. The project provides an X11 backend for the GTK runtime, translating X11 input events into GTK events, mapping GTK drawing to X11 surfaces, and handling window management tasks such as sizing, focus, and decoration. It also supplies theming and font rendering capabilities consistent with GTK applications and supports standard X11 features such as clipboard, drag-and-drop, and selection.

Historically, X11GTK emerged in the early days of GTK development as a means to run GTK applications in X11 environments before broader Wayland adoption. It served as a bridge between the GTK stack and the X Window System, complementing the GDK abstraction layer used by GTK. Over time, GTK's own X11 backend matured and Wayland began to supplant X11 in many distributions, reducing reliance on a separate X11GTK component. As a result, X11GTK is generally described as a historical or archival project, with most contemporary GTK deployments using the built-in X11 backend or modern Wayland.

Licensing and availability varied by version, but the project typically followed permissive or GPL-derived licenses common in the GTK ecosystem. See also: X Window System, GTK, GDK, Xlib, Wayland.