picom

xcompmgr was a demonstration, and anyone who wanted to use it for real had to patch it. Dana Jansens's branch xcompmgr-dana added fading and better shadows; Christopher Jeffrey took it further in 2011 under the name compton, with vsync against the display, per-window-class opacity rules and a GLX backend alongside XRender. When Jeffrey stopped maintaining the code, Yuxuan Shui took over, and in 2019 the project was renamed picom to mark that it was no longer the same program.

Configuration lives in picom.conf, where rules match on window class, name and type: terminals at 90 percent, menus without shadows, full-screen games left entirely alone. Later versions added background blur, rounded corners and, from version 12, animations, which is to say most of what Compiz once did, without being a window manager. That is the whole point: picom runs alongside i3, bspwm or Openbox and does only the compositing. On Wayland it is not needed, because there the compositor is the window manager.