Bazarr is a companion application to Sonarr and Radarr. It manages and downloads subtitles based on your requirements. You define your preferences by TV show or movie and Bazarr takes care of everything for you.
Worked like crap on my server. The UI was slow, and although it seems like a 'fork' of *arr apps, it doesn't use the same framework. It would often crash and in general just never really worked well for me. Hopefully that will change soon. I'd love to give it another shot.