If, like me, you still haven't switched to a "true" GNU/Linux phone such as the pinephone or the Librem 5, chances are you are running android, i.e., Google/Linux.

An OS: LineageOS

To expand the phone lifetime and avoid feeding the data giants, I recommend using LineageOS, a custom ROM (ie an OS) without your phone manufacturer's and google's spying bloat.

If your phone is in this list, installation should be pretty straightforward. If you couldn't find your phone there, don't panic! You may find a version of LineageOS for your device anyway by searching through the XDA-dev forum. It feels a bit weird to download a binary from an online forum, but this seems to be OK in the Android world. Anyway, I did it for my Xiaomi Redmi Note 4, which is not officially supported by LineageOS anymore, and I am very happy with it.

Now, even if you don't install a custom ROM, I recommend using the following apps:

The ultimate list

F-Droid

This is where the organic apps are.

There is absolutely no valid reason not to install F-Droid on your phone. It is a repository of open source applications, i.e., an alternative to the play store, where (most) apps are user-focused instead of personal-data-collecting focused. Just install this APK, and avoid using the google play store at all costs!

The app search engine included in fdroid is notoriously bad. So here's my curated list of recommended apps (and use your search engine to find other apps unless you know the name of the app you are looking for on F-Droid).

Communications

Main use of a phone, right? It used to be, at least.

• FairEmail for... well, emails.
• QKSMS: I am sure you guessed what it does. LineageOS's builtin SMS app is also good, but this one a little more feature rich.
• Conversations or Quicksy are alternatives to whatsapp, telegram and co. Both are user-friendly XMPP clients. The only difference between them is that Quicksy implements a "your phone number is your username and I'll try to find your contacts using your address book " thing that seems to be very popular among non-tech users for some reason. By using bridges (spectrum2, slidge, biboumi...), your thin XMPP client can communicate with Signal, Telegram, IRC, Matrix, Facebook Messenger, Skype…

Calendar and contacts

• Etar: a calendar app that does not phone home to google every time you do something (if you installed LineageOS, you probably don't need it). Nore more forgetting going to your revolutionary anarchist meetings!
• DAVx5: to use your own "cloud sync agenda and contacts" instead of Google's. Note that you need to choose your contacts and/or agenda provider. I personally rolled up my own radicale instance, but there are some hosted alternative out there. Contact me if you want an account on my radicale instance.
• ICSx5: to subscribe to some read-only calendars only available as ICS (I am looking at you, office 365).

Content consumption (sic)

• Fennec: basically firefox, but on fdroid. Automatically bundles ublock origin, which makes browsing the mainstream web almost sufferable. Combined with firefox on desktop and using a Firefox Sync, you'll have bookmarks, history and passwords synchronized.
• Antennapod: great podcast client with discovery from different sources. The large majority of podcasts still use an open format, usable by a lot of different apps. Enjoy while it lasts!
• Feeder: A RSS client. It provides a simple way to get updates from blogs and websites you like. RSS used to be a lot more popular a few years ago than it is today, but the indie web has not given up on it yet (and why should it?).
• Materialistic: A simple frontend for hacker news, the best "social network" out there, (for computers nerds mostly, but if you like maths/science, you might like it too).
• NewPipe: Alternative to the youtube app. Will remove ads, allow you to play audio while the screen phone is sleeping. It is worth adding their own repo to F-droid, since the latest version is often required and fdroid has a sloooow update process (related to their very limited resources and the volunteer nature of their work).
• RedReader: A text oriented app for reddit for your doomscrolling needs. If you find a little too monotone and old-looking, you probably will enjoy Slide more.
• Wikipedia: it is not strictly necessary to use their app to view wikipedia, but I very much enjoy the dark mode it provides.
• Wallabag: A "save to read it later" app. Requires an account on a wallabag server instance. For now, subscriptions to my instance are opened, so go ahead if you wish.

The following apps require you to either set up your own jellyfin instance (a media server), or to have a nerdy pirate friend grant you access to theirs.

• Jellyfin: The main client, full-featured client
• Gelli: A lighter client focused on music

If you use Kodi, its remote control app can also be handy

Maps

• Organic maps: drop-in replacement for google maps. You won't get the reviews for the places you want to visit, so you might miss shops that buy fake 5-start reviews…
• Transportr: works in most places I have visited. The kind of no-bullshit software I love. Type where you want to go, see the possible public transport options. That's it.
• OsmAnd~: Uses a different rendering technique than most map apps, which makes it easier to customize the looks of the maps you are looking at. Very feature-rich. Contributing to open street map is possible direcly in the app. It is quite resource-heavy though, so I tend to prefer organic maps.

Misc

• Syncthing: A general purpose multi device file synchronization app. Unlike dropbox, google drive and the like, this does not use a "cloud"-based drive, but rather relies on direct communication between devices. I use it to sync my phone's pictures to my desktop computer.
• Fitotrack: There are a lot of options for privacy-friendly sports tracking apps on F-Droids, but I settled on this one.
• Aurora Store: OK it might happen that you actually want an app that is only available on the play store (boooooooo). In this case, aurora store got you covered!
• Moneybuster. A "shared budget manager", the app you need to keep track of who paid what during your week-end with your friends. Allows remote sync to #!money so that everyone has access to the same data.
• KDEConnect: Thanks to this, I can write SMSs from my desktop computer. No more using this lilliputian keyboard when I'm home. Has a ton of other features for phone<->phone and computer<->phone interactions.
• Shopping list: very basic shopping checklist app that uses plain text files. I use syncthing to keep its data folder in sync with my SO's phone.

Pfffew that took longer to write than I thought!