AFAIK only Ubuntu and (obviously) Ubuntu-based distributions can handle PPAs. A major (and maybe the only) source of PPAs is Launchpad - another service by Canonical.
A real-world example is Notepadqq. They only provide installation via PPA/Launchpad.
So how can I install them on non-Ubuntu distros like Debian? Can I probably download them (as a .deb file or something similar) manually from the Launchpad site?
You can run this command in Debian Wheezy and newer:
sudo apt-get install software-properties-common python-software-properties
Now, you can use sudo add-apt-repository ppa:some/ppa in Debian!
HOWEVER!
It will not find any packages for you! This is because it is looking for Debian packages, but PPAs hold Ubuntu packages. You need to edit the files located in:
/etc/apt/sources.list.d/YOURPPA/YOURPPA.list
And replace all DEBIAN VERSION occurrences with an Ubuntu version, I suggest Trusty as it is currently the most recent LTS version of Ubuntu.
Now, you can run:
sudo apt-get update
sudo apt-get install YOURPACKAGE
To install the package from the PPA.
Source: WebUpd8 Team
Here is your example - Notepadqq - installed to Debian 10.0.0 Buster.
Although Ubuntu-oriented, in fact the official notepadqq PPA repository does contain .deb files!
(I chose Ubuntu 18.04 Bionic from the technical details dropdown.)
Download both of the following .deb files:
http://ppa.launchpad.net/notepadqq-team/notepadqq/ubuntu/pool/main/n/notepadqq/notepadqq-common_1.4.4-1~bionic1_all.deb
http://ppa.launchpad.net/notepadqq-team/notepadqq/ubuntu/pool/main/n/notepadqq/notepadqq_1.4.4-1~bionic1_amd64.deb
Install via terminal as follows:
sudo dpkg -i ./notepadqq-common_1.4.4-1~bionic1_all.deb
sudo apt-get install -f
sudo dpkg -i ./notepadqq_1.4.4-1~bionic1_amd64.deb
sudo apt-get install -f
Success! ( See: /usr/share/applications/notepadqq.desktop)
