This is extremely Linux only due to the dependency on v4l2loopback and obs-v4l2sink, though, as mentioned below, CatxFish has also written a similar plugin for Windows. I have not tried it, YMMV.
Wanna composite your face (as a video, from your webcam), on top of a video of your choosing, and use that for your conference calls? NOW YOU CAN! (Zoom only supports still-image virtual backgrounds. BOO.)
Note: you will need a greenscreen for this. (You can try all the software-y bits below without one, but it won't look very good at all.) $60 on Amazon, you can probably find one cheaper. (Or make. Or, honestly, it might work if you