yt-dlp for downloading videos from various websites.

qBittorrent for a lightweight and open-source BitTorrent client.

Calibre for organizing, converting, and syncing eBooks.

Jellyfin for a free and open-source media server and suite of multimedia applications.

Sonarr for a PVR for Usenet and BitTorrent users that can monitor multiple RSS feeds for new episodes of your favorite shows.

RetroArch for a frontend for emulators, game engines, and media players with support for various platforms.

Radarr for an independent fork of Sonarr reworked for automatically downloading movies via Usenet and BitTorrent.

Tachiyomi for an Android app for reading manga from various sources.

Transmission for a fast, easy, and free multi-platform BitTorrent client.

Musicbrainz Picard for fetching music metadata and standardizing file naming schemes.

Stremio + Torrentio for a media center that allows you to watch movies, series, live TV, and more with the help of torrents.

Nicotine+ for a graphical client for the Soulseek peer-to-peer network.

gallery-dl for a command-line program to download image galleries and collections from several image hosting sites.

jdownloader2 for a free download management tool.

Readarr for a fork of Radarr for eBooks and Audiobooks.

ffmpeg the Swiss army knife for everything video and audio.

Prowlarr for a meta-indexer that integrates with other applications like Sonarr, Radarr, and Lidarr.

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

Overseer for a request management and media discovery tool built for the Plex ecosystem.

Bulk Rename Utility

Plex. I know it’s not the open source option, but I love it.

mediainfo Know everything about your medias.

Czkawka for finding duplicate files and similar images.

ShareX for capturing and sharing screenshots, recordings, and other files.

Jackett for a single indexer API for multiple torrent trackers.

aria2 for downloading files.

mkvtoolnix create/edit mkv files. Very useful to remove or add subtitles or audio tracks amongst others.

deluge

mldonkey cross-platform multi-network p2p daemon

Navidrome for a self-hosted music server and streamer compatible with Subsonic/Airsonic clients.

Lidarr for managing music collections for Usenet and BitTorrent users.

Bazarr for managing and downloading subtitles as a companion application to Sonarr and Radarr.

Romm for game collection and roms (it supports PC games aswell)

Tellico for a KDE application for organizing your collections, including books, videos, music, and more.

Tixati is an alternative torrenting program that I switched to from QBitorrent.

rtorrent great to download torrents especially on a server.

hydrus for a desktop application for managing a personal collection of images, videos, and other files.

(didn't see you posted this one as I was posting it)

yt-dlp youtube-dl fork that is more current and works better for tons of sites to download media.

Deluge run headless. Great Android mobile app.