Kavita for eBooks and Manga

eMule for a classic P2P file-sharing software with a large user base.

Spotiflyer downloads playlists from Spotify and many other services.

DupeGuru for finding duplicate files on your computer.

TMSU for a command-line tool for tagging your files and accessing them through a virtual filesystem.

Tautulli for monitoring and tracking your Plex Media Server usage and performance.

Ombi for a self-hosted web application that allows users to request content for Plex, Emby, or Jellyfin.

Fopnu for a P2P file-sharing system with no ads, no spyware, and no bundled software.

beets music library management and tagging for geeks

digikam for image and video collection management and viewing (also does duplicate detection)

FrostWire for a BitTorrent client and media player with built-in search functionality.

Plex for Movies / Shows / Music.

eiskaltdcpp for a cross-platform program that uses the Direct Connect and ADC protocols.

Stash for organizing and serving adult video and image files.

Media Center Master the free version is a cool utility for organizing movies/TV shows that will find and attach metadata. The premium license unlocks torrent/Usenet integration and will automatically find download new episodes or movies as they come out based on your preferences

mediarepo for a media manager similar to image boards (boorus), allows tagging media and searching using those tags.

Mylar3 for an automated Comic Book (cbr/cbz) downloader program for use with NZB and torrents.

SuperTag for a command-line tool to manage files using tags instead of folders.

LaunchBox for a game launcher and organizer for Windows.

LazyLibrarian for following authors and grabbing metadata for digital reading needs.