The two technologies are used to sandbox GUI apps. They were supposed to make it possible to run newer apps on top of older libraries and to let 3rd party edito

The two technologies are used to sandbox GUI apps. They were supposed to make it possible to run newer apps on top of older libraries and to let 3rd party editors publish their software easily towards multiple distributions, but in practice you can face many problems (lack of system integration, apps not even starting, ...). Flatpak allows anyone to create stores, (iirc Flathub code is on Github) while with Snap you need to use the Snapcraft (vendor lockdown).