Jackett
Jackett works as a proxy server: it translates queries from apps (Sonarr, Radarr, SickRage, CouchPotato, Mylar3, Lidarr, DuckieTV, qBittorrent, Nefarious etc.) into tracker-site-specific http queries, parses the html or json response, and then sends results back to the requesting software.
one-liner command to install it on Linux as a service:
User needs to be in sudoers as this is system service that will be installed (systemctl status jackett.service)


cd /opt && f=Jackett.Binaries.LinuxAMDx64.tar.gz && release=$(wget -q https://github.com/Jackett/Jackett/releases/latest -O - | grep "title>Release" | cut -d " " -f 4) && sudo wget -Nc https://github.com/Jackett/Jackett/releases/download/$release/"$f" && sudo tar -xzf "$f" && sudo rm -f "$f" && cd Jackett* && sudo ./install_service_systemd.sh && systemctl status jackett.service;cd - && echo -e "\nVisit http://127.0.0.1:9117"
Then visit http://127.0.0.1:9117