Love distrobox. Use it on my daily driver. If you are running an Ubuntu LTS / Debian stable / PopOS as your main operating system (because you want stability), but want to run bleeding-edge gui applications in debian testing (or even unstable) in an isolated container, you can. Running GUI applications in Linux containers is usually non-trivial to set-up, but distrobox makes it painless. Install with apt, export to the host operating system with 'distrobox-export --app blah'.
It's pretty much the same from the outside; the difference is how the containers are built and managed. Flatpak uses OSTree with custom build scripts, while distrobox uses Dockerfiles and more standard packaging.
