Calibre-Web is a web app providing a clean interface for browsing, reading and downloading eBooks using an existing Calibre database.
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.