for Mac is distributed as a mountable disk image (.dmg) file.
After it is downloaded, it may appear on the desktop as a
pseudo-disk, or you may have to drag it to the desktop from your
downloads directory. Run Panini-Pro direct from the
pseudo-disk, rather than copying it to applications, since you will be
replacing it often. Dragging the desktop disk to the trash
dismounts it but does not delete the .dmg file from your downloads
To remove a version just delete the .dmg file from the downloads directory.
There is some documentation on the .dmg in docs/, but best to check the website for updates.