Whats your must-have FOSS app?

F-Droid for FOSS apps
Aurora for Google Playstore apps
OSMAnd for navigation
Oeffi for public transport
many Simple Mobile Tools apps
K-9 Mail
Tor browser
Shelter for isolating apps
Tusky for Mastodon
Jerboa for Lemmy
Nunti for RSS feeds
Molly for Signal
Telegram FOSS
Aegis for 2FA
QickDic (dictionary)
TinyWeather
Threema Libre (not free)

LineageOS: my Android ROM of choice
LineageOS for MicroG: the ROM on my second phone where I quarantine my use of apps that refuse to work without Google services (mostly stuff I need for business travel e.g. Amtrak, Google Maps)
Aurora Store: allows installation of most Play Store apps without login. I mainly use this on the MicroG phone, but it's also needed to get the ProtonMail and ProtonCalendar apps (only ProtonVPN is on F-Droid)
TrackerControl: allows fine tuned domain blocking on a per-app basis. Often allows you to block just ads and trackers but still be able to use an app or at least many of its features.
Arcticons: monochrome line art icons (because I hate fun and want my GUIs to look like a terminal)
AsteroidOS Sync: WearOS replacement. AsteroidOS still has a long way to go, but I doubt WearOS would play nicely with LineageOS and I don't want all the tracking anyway.
Bubble: bubble level by woheller69 (a true F-Droid GOAT)
FlorisBoard: afaik, only FOSS gesture typing Android keyboard (besides AnySoft, which doesn't seem to work consistently)
GMaps WV: fairly locked-down web viewer for Google Maps (sadly OSM just doesn't have a usably complete business directory where I live)
Lawnchair: launcher with all the features I want except being up to date on F-Droid
Librera: the PDF reader on F-Droid that I hate the least. (Anyone got any better recommendations?)
NewPipe: ad-free Youtube player with locally stored subscriptions and playlists. An IzzyOnDroid fork with SponsorBlock is also available.
QKSMS: my SMS app of choice
Signal: because I can't convince my friends to switch to Briar
SpoTube: pirate ad-free Spotify that works by looking up tracks on Youtube. Is therefore limited by what's available on YT and sometimes plays wrong tracks, but you can't beat the price :] Even interfaces with a Spotify account to play and edit playlists.
Standard Notes: E2E encrypted cloud-synced notes. Also accessible by web browser, which has saved my ass a few times while phoneless
Weather: by BeoCode on F-Droid
VLC: everyone's favorite traffic cone boi

Bitwarden

I've seen Bitwarden show up in this thread a few times. I've been a longtime user of KeePassX. Is there any particular reason I should consider switching?
- What made me choose bitwarden is the emergency access feature.
  It allows to designate someone as an emergency contact. This person can request access to your vault and if you don't deny the request then they will have access after x days.
  This way, if something happens to me then someone in my close family can still access my account.
  I got the case recently with my brother in law who got into an accident and thanks God his laptop was not locked so my sister could access his accounts.
  Because if not it can be a nightmare ! Having to deal with all the utilities company, harassing you because you did not pay the bill that arrived on a locked email account, then not being able to pay the bill anyways because you have to connect on they website ... on top of getting your husband and the father of your child in the hospital in a coma.

Quillpad (offline notes)
MuPDF mini (Great simple PDF reader)
Unit Converter Ultimate (lots of various conversions)
Retro Music (fdroid repo for pro version, best music player hands down)
OSMAnd (Great for fancy mapping features)
Mull (hardened Firefox with the quickest updates of all Firefox based browsers)
AntennaPod (best podcast app)
Obtanium (install apps easily from sources such as Github)
Droid-ify (better fdroid)

Ankidroid— Create, share, borrow and study with flash cards

Firefox— Web browser

Rethink Firewall— Best firewall for android

Infinity— Gonna miss this one (Reddit client)

Libretube— Modern Youtube client using Piped

Obtainium—Keeps track of all my foss apps from their git repositories + them

Gnu IMP— Desktop photo editor

Aurora Store— Download apps from the play store

Thanks for recommending Libretube. I just switched to GrapheneOS and was looking for a FOSS revanced replacement without the need for Play Services or MicroG. Libretube is absolutely perfect.

Firefox, LibreTube, Kaiteki

KDE Connect means that I can ping my phone that's usually presumably somewhere behind my bed or on a counter somewhere, without having to sheepishly walk to the nearest person and ask "can you call my phone I lost it :c"

Fedilab for Mastodon (an alternative to Tusky)
Jerboa for Lemmy
LibreTube for usable YouTube without an account
FluffyChat for Matrix (an alternative to Element)
FairEmail for mails
Molly for Signal (pretty much the same as the original app)
Forkgram for Telegram (also pretty much the same as the original open source version)
Aurora for PlayStore apps
F-Droid
Fennec for browsing (the opener version of Firefox)
Aegis for 2FA (an alternative to Google Authenticator)
KeePassDX for passwords (an alternative to Keepass2Android)
OpenKeychain for PGP Keys
Orbot for connecting to Tor and running a Snowflake proxy
RethinkDNS as DNS with blocklists, firewall and routing to Orbot via Proxy for all TCP connections
Tutanota as synchronized calendar
Osmand~ for navigation (an alternative to Google Maps)
Transportr for public transport (an alternative to DB Navigator in Germany)
In general the "Simple ..." apps on F-Droid are also nice

I'll be in Germany next month, so I'll have to try out Transportr

Syncthing is the one, I could probably replace any one but this one.

+1 for k9. Lightweight nd functional.

Some from the ones I use:

F-Droid
Fennec (firefox variant that supports custom addon collections)
K-9 Mail
Termux (terminal + Linux environment)
Jerboa for Lemmy
Wikipedia

You should check out iceraven if you want even more addons. Iceraven
- Apperantly the addons are taken from this collection, which can be set up on fennec as well

Bitwarden, Signal, Firefox, Sumatra PDF, Standard Notes, andOTP, and VLC Media Player

Love all of these, but really happy to see Sumatra PDF because that thing is just incredible and is a day 1 install on a fresh OS.
- Its one of the first things I install too! A really efficient piece of software!
Isn't andOTP basically dead? The app is unmaintained at this point and last update was 2 years ago.
I think something like Aegis Authenticator is a better option nowadays.
- Yes, I should really switch to Aegis. andOTP has been working well for me though.