NzbGet is a solid long-time usenet downloader. There are others, but i will focus on this one.

NzbGet has an ebuild for Gentoo, so installing it it's a simple emerge:

emerge -v nzbget

As usual move the home folder to /data/daemons/nzbget:

usermod -m -d /data/daemons/nzbget nzbget

and add the nzbget user to the media group:

usermod -a -G media nzbget

One last required step is to ensure that the other tools can access the nzbget folder (to reach the download folders inside), so:

chgrp media /data/daemons/nzbget

To be more consistent, and to prevent future overwrite onupgrade, you should move the default configuration file for nzbgetd to the nzbget home folder too:

mv /etc/nzbgetd.conf /data/daemons/nzbget

You need to do some fine tuning to the /etc/conf.d/nzbget file. Put the following content in it:

# Which user to run nzbget as
NZBGET_USER="nzbget"
NZBGET_GROUP="media"
# Location of config file
NZBGET_CONFIGFILE="/data/daemons/nzbget/nzbgetd.conf"

Note that you have:

• replaced the default group for the daemon to media
• specified the new location for the configuration file

Before you proceed, you should make NzbGet web accessible via the reverse-proxy, so that access, configuration and usage will be simplified from the beginning.

Add this file to /etc/nginx/folders:

nzbget.conf

# NZB Get
location ~ ^/nzbget($|./*) {
        rewrite /nzbget/(.*) /$1 break;
        proxy_pass http://127.0.0.1:6789;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
}
location ~ ^/nzbget$ {
        return 302 $scheme://$host$request_uri/;
}

Add the setup to the Reverse Proxy and reload it. Check The Reverse Proxy concept for more details.

Now, setup the daemon to start at boot, and start it now:

rc-update add nzbget default
/etc/init.d/nzbget start

Every download client needs to be integrated in your other tools. Unfortunately, you need to do it by hand for every tool.

Every *Arr's tool has the same settings → downloaders section that you can populate with the downloaders. Tap on the plus button and add the downloader. Test it before saving.

Prowlarr is a special case: you only need to define the downloader IF you plan to search from the Prowlarr web GUI, otherwise it's not needed. And no, Prowlarr will not synchronize your downloader to the other *Arr's, like it's done for indexers. Sad, but that's the way it is.

Head to 10.0.0.1/nzbget from which you add your manual downloads or manage the automatic downloads added by the other tools.

To securize your NzbGet installation go to settings → security and specify 127.0.0.1 as ControlIP. In the same page you also must set the umask to 0002 so that the other tools will be able to fetch the downloads from NzbGet.

You will need to add here your Usenet access providers under settings → NEWS-SERVERS. Remember that Usenet is different from torrents. You will be able to download only one file per server at any given time, no matter how many connections you have on that server. This is because files are chunked in many pieces and NzbGet will saturate all your connections to that server to retrieve in parallel as many chunks as possible. To download more than one file at the same time, you need more than one server configured.