Here’s one I know. Creates aesthetic wavy things.
It is an HTML/JS pair, so it would require some wrangling to get it to write to a file instead of an HTML canvas. Though it looks like someone translated it to Python with file output here. (I have not tested this.)
My personal bugbear is that there is no compositor-agnostic way to tell what workspace a window is located on. This means that taskbars cannot implement an “only show windows on the current workspace” setting, which frustrates me to no end. (Taskbars like the LXQt and XFCE panels still have the setting, but it does nothing.) There is not even any proposed protocol to support this, and acceptance and implementation would take years even if there were.
Integrated desktops like KDE probably roll their own custom implementation, but out in Labwc land I’m shit out of luck. (1 2 3 4)