Not a direct alternative per se, as it is meant for coding, but https://syphon.github.io/ https://syphon.github.io/ - I used to use this years ago and it worked

Not a direct alternative per se, as it is meant for coding, but https://syphon.github.io/ https://syphon.github.io/ - I used to use this years ago and it worked great then for screen captures.