Do you mean Flatpak?

Still no though.

Not Flatpak, not Snaps.

AppImages are a completely different spec for distributing packages. All you do is download, run chmod u+x <name>.AppImage and you are off to the races. My understanding is Flatpak doesn't work the same way.

Apart from being unwillingly force fed Snaps by Ubuntu I've never ran into them in the wild. It seems like they have no traction whatsoever.