Broadway (GTK)

Alexander Larsson at Red Hat built Broadway in 2010–2011 as an experiment and landed it in GTK 3.2. GDK, the layer that hides the window system from the rest of GTK, had just gained support for several backends in one build, and Broadway was the proof: set GDK_BACKEND=broadway, start the broadwayd daemon, open localhost:8080 in a browser and there is the program, menus and dialogs included, without a line of it changed. In GTK 3 the differences between frames were sent as images; in GTK 4 the backend was rewritten so that GSK's render nodes are translated into DOM elements instead, which keeps text sharp and traffic down.

Use stayed narrow: demos, a quick way to show a tool on a server without X, and speculation about GTK in the cloud that never became more than speculation. The limits are built in: one browser per display, clipboard and drag-and-drop that only partly reach through, and no access control beyond listening on localhost. But as an argument that GDK's abstraction held up, it was persuasive, and the Wayland backend came in the same way in the same release.