This is a Debian package repository that is used on KristShell's Debian and Ubuntu systems.
It contanins Free Software packages that are either not in Debian or packages that we for one reason or another need to upgrade to a version that is newer than the version in the stable debian release.
The easy way to add this repo is to download and install the latest repository package using «apt install ./package.deb».
That will add the kristshell repo in /etc/apt/sources.list.d/kristshell.list and also will add the signing key. It will also add the sources repo that contains the sources for all of the packages in our repository.