If you are specifically looking for "Solid Paper" in relation to DoublePane, it appears there might be a mix-up with wallpaper or design tools like or Bumpy Paper . Quick Access & Alternatives
DoublePane is a window management application for macOS that allows users to quickly position windows side-by-side using keyboard shortcuts. While historically a paid app, it has been listed as on the Mac App Store at various times. DoublePane for Mac Free Download
: A free, open-source utility for spreading high-resolution images across multiple displays, available via GitHub or Reddit . News and Tips for Mac, iPhone, iPad, and Everything Apple If you are specifically looking for "Solid Paper"