F-Droid.org is just a repo out of hundreds of repos created by individuals all around the globe. With the tools of F-Droid, everyone can create their own repo. So whether you are a musician who wants to publish their music or a developer who wants to serve nightly builds of their app, you are free to create your own repo and share it with other people independently of F-Droid.org.
In the past, creating a repo has been difficult because you had to have knowledge on the command line, needed to edit text files to edit your packages’ store details and had to paste screenshots in a special system of directories to have them served well inside the F-Droid app.
This all got easier now: with Repomaker, you are able to create your own repo and do not need to have any special knowledge to do so. Check out the installation guide for information on how you can install Repomaker on your device.
Like any other project of F-Droid, Repomaker is free and open source software. You can find the source code and its license on gitlab.com.