Flatpak
Flatpaks provide access to the wider Linux ecosystem through Flathub. They operate entirely in user space, store system-wide installations in /var/lib, respect the immutable root, and are the recommended path for mainstream GUI applications.
Documentation
Flatpak Documentation: https://docs.flatpak.org/en/latest/
Information
Users who want to use bleeding-edge Flatpaks can enable the Flathub-beta channel. Do it at your own risk.
flatpak remote-add --user flathub-beta https://flathub.org/beta-repo/flathub-beta.flatpakrepo