The same Pen Pal, running as an application on your own machine. Your projects are ordinary folders of files on your own disk, and they open, save and print with no connection at all.
Download for macOSDouble-click the download to unpack it, drag Pen Pal into your Applications folder, and open it the ordinary way. This build is signed with an Apple Developer ID and notarized by Apple, so macOS opens it without warnings or workarounds.
It asks once for permission to reach your Documents folder, because that is where it keeps your projects.
When a newer version exists, Pen Pal notices it at launch and offers it to you. Choosing to install saves your work and backs it up first, then replaces itself and restarts. You never have to come back to this page.
Each update is signed, and the copy on your machine checks that signature before it will replace anything, so nothing but a real Pen Pal build can ever install itself.
Every project is its own folder of plain files, one per page, kept in a Pen Pal folder inside your Documents. You can open, copy, move and back them up without Pen Pal, and nothing about them needs this application to stay readable. Choosing a different folder is in the next build.
An account is optional. Signing in adds a second copy in the cloud and lets you pick the same project up on another machine. The copy on your disk stays the one that counts.