Jackett works as a proxy server: it translates queries from apps (Sonarr, Radarr, SickRage, CouchPotato, Mylar, DuckieTV, etc) into tracker-site-specific http queries, parses the html response, then sends results back to the requesting software.
NZBHydra is a meta search for NZB indexers. It provides easy access to a number of raw and newznab based indexers. You can search all your indexers from one place and use it as an indexer source for tools like Sonarr, Radarr or CouchPotato.
Sonarr is a PVR for Usenet and BitTorrent users. It can monitor multiple RSS feeds for new episodes of your favorite shows and will grab, sort and rename them. It can also be configured to automatically upgrade the quality of files already downloaded when a better quality format becomes available.
Radarr is an independent fork of Sonarr reworked for automatically downloading movies via Usenet and BitTorrent.
The project was inspired by other Usenet/BitTorrent movie downloaders such as CouchPotato.
Overseerr is a free and open source software application for managing requests for your media library. It integrates with your existing services such as Sonarr, Radarr and Plex!