I needed some more bench space in my work room, so I wanted to move my keyboard up to being attached to my monitor. I had some spare 3/4" dowel rod handy, so I modeled a screw clamp and an arm that could mount to it and hold a 200mm deep keyboard. The arms were a tight enough press fit on the dowels, but I added some 4mm screws and nuts just to be sure.

Had to adjust the gas spring in my monitor arm to accept the weight, but after that, it works like a charm.

I suppose technically it's not explicitly a VESA mount, since it's just some screw clamps and could be mounted to just about anything. But this was my use case.