Flathub

Flathub aka Flatpak aka xdg-app

Flathub is a central Flatpak repository.

Flatpak was formerly called xdg-app are the software available from Flathub as well as other sources.

Flatpak is a package format that works and is supported on most major linux distributions.

Snap aka Snapcraft is an alternative to Flatpak. They essentially are competing systems to provide the same thing. Both are part of a concept where version control of dependencies is handled by a great deal of redundancy. Rather than having binaries compiled for a specific linux kernel, distribution, and libraries, the pack contains redundant copies of all dependencies necessary for the specific compiled version of the binary itself.

Bloatware - an example where the efficiency of the linux architecture is bypassed for the purpose of simplifying the application developer's burden to create compatible binaries for various distributions -or- make it unnecessary for the end user to have to compile a software from source.