The list is organized in alphabetical order, if not specified otherwise.
I) Programs
i.1) Audio / Music
i.2) Image / Video
i.3) Communication / News
i.4) Personal planning
i.5) Knowledge Management / Document preparation
i.6) General
II) Online Services
ii.1) Email Providers
ii.2) Search Engines
ii.3) Web Browsers
ii.4) Content curation
ii.5) Content sharing
ii.6) Cloud storage
ii.7) Games
ii.8) Others
I) Programs
i.1) Audio / Music
FFmpeg - tools for transcoding, streaming and playing of multimedia files.
FLAC - lossless audio coding format.
Pulsemixer - mixer for PulseAudio.
Ogg Vorbis - lossy audio coding format.
Opus - lossy audio coding format (preference: 128-160 VBR).
Quod Libet - audio player, tag editor and library organizer.
i.2) Image / Video
OBS - video recording and streaming.
Webp - image format (replacement for JPEG, PNG, GIF).
i.3) Communication / News
Newsboat - rss/atom feed reader.
Rate.sx - cryptocurrencies exchange rates.
i.4) Personal planning
Calcurse - text-based calendar and todo manager.
GNU Pem - personal expense manager.
Keepass XC - password manager.
Ledger - double-entry accounting system.
Taskwiki (vim plugin)- integration of taskwarrior with vimwiki.
i.5) Knowledge Management / Document preparation
BibTeX - lists of references (works well with LaTeX).
Groff - document preparation system.
LaTeX - document preparation system.
Libreoffice - office productivity suite.
Mdp - markdown presentation tool.
NovelWritter - text editor for writing novels and larger projects.
Vimwiki (vim plugin)- note taking.
Xapers - personal document indexing system, geared towards academic journal articles.
Zimwiki - note taking (alternative to vimwiki).
i.6) General
Bc - GNU bc arbitrary precision calculator language.
Cht.sh - cheat sheets repositories.
Rofi - window switcher, application launcher and dmenu replacement.
II) Online Services
ii.1) E-mail Providers
Displayed in order of preference. I have used all of those (many more actually), and all here offer a good service overall.
Posteo - open-source, secure, eco-friendly, cheap.
Countermail - a bit more expensive alternative, more oriented towards security.
Snopyta - free open-source service, but more limited email functionality.
Tutanota - free open-source service.
Automario - free open-source service.
ii.2) Search Engines
Brave search - can be used independently of Brave browser.
DuckDuckGo - most known out of the list.
Little Isle - stock SearX with a Wiby template.
Metager - based on principles of free knowledge, open-source, anti censorship, and renewable energy.
SearX - privacy-centered (many instances to choose from).
Yacy - built on principles of peer-to-peer networks.
ii.3) Web Browsers
Librewolf - fork of Firefox, focused on privacy, security and freedom.
Links2 - text and graphic web browser with a pull-down menu system.
Netsurf - lightweight and portable (more restricting than the others, for privacy reasons).
Qutebrowser - uses Vim-style key bindings and a minimal GUI.
W3m - text-based web browser and terminal pager.
Freenet - peer-to-peer web platform (clearnet alternative).
Tor - great for privacy (clearnet alternative).
ii.4) Content curation
Coursera - some free online courses from various schools (proprietary).
Dead Sea Scrolls - digital library.
edX - some free online courses from various schools (proprietary).
Encyclopedia Britannica - alternative to wikipedia (proprietary).
Librivox - free public domain audiobooks.
Petrolette.space - rss reader on your browser.
Project Gutenberg - library of public domain ebooks.
Standard Ebooks - public domain ebooks that are carefully formatted.
Research Rabbit - tool to discover research papers (proprietary).
DeepL - translation tool (proprietary alternative to google translate).
Lingva Translate - a FOSS front-end for Google Translate.
Libre Translate - translation tool.
SimplyTranslate - translation tool.
ii.5) Content sharing
Ambient Mixer - listen and mix royalty-free ambient sound.
Codeberg - software development platform.
Font Squirrel - collection of fonts.
Freetube - private youtube client for desktop.
Hedgedoc - platform to write and share markdown.
Incompetech - royalty-free music.
Inventaire - book inventory and sharing.
Invidious instances - front end for youtube.
Jitsi Meet - video calls and conferencing.
KissccO - library of free-usable images.
Neocites - web hosting service.
Peertube - decentralized video platform.
Pickup Image - library of free-usable images.
Pixelfed - photo sharing platform.
p2p.chat - peer-to-peer video conferencing application.
Unsplash - library of free-usable images.
ii.6) Cloud storage
Cryptee - encrypted service to store notes, documents and photos.
Filen - encrypted cloud storage.
The Good Cloud (Nexcloud host).
ii.7) Games
I'm not a gamer, but I'm adding these in case you want some break from work.
Freesweep - minesweeper (cli app).
Nsnake - snake game (cli app).
You can also find more games here:
ii.8) Others
Museopen - free music recordings, sheet music, apps, and educational materials.
Overleaf - online LaTeX editor.
Liberapay - donations platform.
LibreSpeed - speedtest (no flash, java, or websocket).