https://alternativeto.net/ (The website is not FOSS but they list all kinds of alternatives to many things that are open source)

Linux, or as I've recently taken to calling it, Linux.

Newpipe, I can see YouTube and download the audio and video if I want and I can see it without ads

It might not be an obvious one but GIMP.

Adobe are ripping off my work and violating my clients privacy if I use Photoshop to process their images. So I use GIMP instead.

Same of my favorites:

Catima (Loyalty Card & Ticket Manager for Android)

Gadgetbridge (A free and cloudless replacement for your gadget vendors' closed source Android applications)

Heliboard (keyboard)

Jellify (music client for Jellyfin)

Jetbird (client for Netbird)

Jellyfin (media system)

Lissen (client for audiobookshelf)

LocalSend (open-source cross-platform alternative to AirDrop)

Obtainium (install and update apps directly from their release pages)

OSS Document Scanner

Tusky (client for mastodon)

Voyager (client for Lemmy)

PC / General:

• Nextcloud with Collabora Office CODE Server for Filesync and Online editing. I also setup STUN and TURN for Nextcloud Talk, which I use to groupcall friends for virtual board game nights. And I use Deck as a Kanban-Board.
• Bitwarden/Vaultwarden - I do not need to say more, I think.
• Firefox + uBlock Origin. This combo also works on mobile, so.... Good Bye ads!
• Thunderbird. Also available on Android. Though Thunderbird Mobile is the same as K9 Mail, but reskinned IIRC.
• PiHole (at least in my home network). Same as above, but also (somewhat) blocks ads in proprietary apps/devices. Even works on the ad supported tier of streaming services to at least reduce ads.
• SearXNG - Meta search engine, that you can self host. There are public instances, but if you want full control over the available feature set/ available search engines, etc. just host it yourself.
• I host a private instance of an unofficial open source web app of the board game Terraforming Mars, as one person in our game group has incompatible hardware for the official implementation. One of the options for the mentioned virtual board game nights.
• Jellyfin. My BluRay Player died. I had most of my library ripped anyways, so... I finally got around to set it up.

On Android:

• DAVx5 and ICSx5 to Sync contacts and calendar with my Nextcloud.
• Etar Calendar. It's a simple calendar. Just a simple "no bullshit" app. I like it.
• Firefox/uBlock Origin/K9 Mail
• Signal/Threema/SchildiChat(Matrix) - secure messengers
• OSMAnd/Street complete/Organic Maps - all three are Open Street Map apps. OSMAnd is the killer-app that does everything. Organic Map for a more streamlined experience. Street complete, to quickly contribute to OSM by doing "quests" (= answer questions) in your surroundings to fill in incomplete data. (Street names, types of streets, house numbers, opening times, is X still here?,...)
• Shattered Pixel Dungeon. Roguelike Dungeon Crawler, high quality. Looks easy, but hard to master.
• Lichess - Chess app/plattform.
• Öffi - Germany centered, but also somewhat usable in other places. Open Source public transit app, with many integrations of local and national networks. The developer has had some problems with Google and their app review process (IIRC regarding donation instructions?), so better to get it from FDroid, where updates are not blocked by some company policy...

• Memos
• PaperlessNGX
• Jellyfin
• Beszel
• Stalwart
• Adguard-home
• Fresh-RSS
• Nextcloud
• Corteza
• Vaultwarden
• Navidrome
• Immich
• Matrix (Conduit)
• Romm
• Searxng
• Mealie
• HedgeDoc
• Vikunja

AntennaPod

Android:

• Cake Wallet - crypto assets
• CoMaps - navigation
• Cryptomator - encrypted files
• LibreraFD - ebook reader
• Retro music - local music player
• SimpleX - chat
• Syncthing - sync between my phone and computers

Debian, KDE, KeePassXC, FreeTube, kdenlive, Audacity, GIMP, Krita, Blender, Geany, DeskFlow, RustDesk, F-Droid... just off the top of my head

PC:

• Firefox
  • uBlock Origin
  • History Helper
  • SingleFile Web Archiver
• spotify_player CLI Spotify Player by Rust
• RipGrep
• RSS Guard RSS Reader

iOS:

• KDE Connect File Transfer

Web:

• ListenBrainz Last fm FOSS Alternative
• Lemmy Reddit FOSS Alternative

Portmaster on desktop, InviZible Pro on mobile

My own link collector, mostly.

Tubular, a fork of NewPipe with SponsorBlock and Return YouTube Dislike integration! Use it all the time lol, probably too much

Immich

Jellyfin

*arr suite

Mealie

Authelia

Aegis

Liftlog

Syncthing

Aves Libre

Gadgetbridge

Lemmy

Forgejo/codeberg

I use librewolf for browsing (with the temporary containers addon), nheko for matrix, thunderbird (of course).. that has pgp functionality built in.

When it comes to web browsing I think it is a good idea to use more than one browser. For most general use stuff I use librewolf and already mentioned. I do all my work related stuff, banking and purchasing in chromium. Unfortunately we're back in the days of internet explorer when a lot of mainstream sites are broken and only work well on one browser. But the uses I mentioned are not as important in regards to privacy so it works for me.

Crypto sites are also often to be built for a chromium base, but I like to keep those separate and use Brave for that.

keepassxc+nextcloud

Pfblocker. This one is yuuuuge.

Lineage.

Unlock Origin Nextcloud OpenVPN Unbound Exim

Then the fun stuff, jellyfin, zoneminder, etc.

• Breezy Weather
• Organic Maps
• RadioDroid
• ~~Higgsters (lite ad-free games like solitaire and boggle)~~ oop not open source. Free and private tho afaik

Not favourite but very useful these last two months for losing some weight.

Trale, it does one thing and it does it well. Keeps track of body weight and makes a graph.

FitBook, for counting calories. I think it can do some other things but I only use it for that.