What would you need an addon for? If you enable the clipboard monitor, jdownloader automatically adds all downloads it finds from any link you copy.
Edit: If you don’t like the clipboard monitoring you can also use the Open With addon to explicitly add links.
If you just want to use it from your home computer / network you can run it locally, either installing it directly or in a container. You only need a server (or a way to connect to your home network) if you want to access it from elsewhere.