Maybe the could just offer a way to download the apps via the internet, and then open some kind of image container and move a file to the Applications folder.

This is inherently inferior as you are requiring the user to make the distinction between safe and unsafe software each and every time they install software something users are notoriously bad at.

Additionally it makes it hard for 2 apps to specify libraries required meaning each must include whatever they require AND either updates are manual, read nonexistent, or each app includes its own nagging update mechanism.

An account could be required for installation of non free software while still allowing installation of free software without it.