

This, in turn, is different from APT, which is not Debian’s repository, but Debian’s package manager. So, technically, I could write “sudo apt install (anything)” to get any piece of software from Debian’s repository indeed, but I could also use that command to get software from somewhere else also in the form of a Deb package but which would not have come from Debian itself.
With apt (and discover which uses apt/dpkg at the background) you can install anything from repositories configured on your system. So, if you want to use apt to install packages not built by Debian team you’ll need to add those repositories in your system, so they don’t just appear out of nothing.
Some software vendors offers .deb packages you can install which then add their own repository on your system and then you can ‘apt install’ their product just like you would on native Debian software and the same upgrade process which keeps your system up to date will include that ‘3rd party’ software as well. Also some offer instructions on how to add their repository manually, but with a downloaded .deb it might be a bit easier to add repository without really paying attention to it.
Spotify is one of the big vendors who have their own repository for Debian and Ubuntu and with Ubuntu there’s “ppa” repositories, which are basically just random individuals offering their packages for everyone to use and they are generally not going trough the same scrutiny than official repositories.


And that’s exactly why it’s called Krita. Also it was previously called ‘Krayon’, so they just kind of kept the name.