Droid-ify is a much nicer client for F-Droid.

Obtanium for downloading apps from various other sources.

Aurora Store for anonymously downloading apps from the Play Store without a Google account

LibreTube or NewPipe for watching YouTube videos without ads or tracking.

Seal for downloading YouTube videos.

Retro Music Player - probably the best looking music app for Android.

Pano Scrobbler - a FOSS app for Last.fm, Libre.fm and Listenbrainz. (I recommend Obtanium to download it from GitHub.)

Murglar for downloading Music in full quality from Deezer.

Molly - a better Signal client. (You can use Obtanium to download it from GitHub, you can add their F-Droid repo or download it using Accressent, a new experimental app store that seeks to replace F-Droid.)

Gallery - a simple gallery app that looks good and respects your Material You theme.

Element X is a much better Matrix client than the standard Element app. (I recommend downloading it from GitHub using Obtanium.)

LinkSheet - a small app that restores the old Android URL link chooser. It has many great features like the ability to remove tracking parameters from URLs or using FastForward to annoying bypass URL shorteners.

UntrackMe - a tool that can redirect YouTube, Twitter, Reddit, etc. links to privacy-friendly alternative frontends like Invidious or Piped for YouTube, Nitter for Twitter and LibReddit or Teddit for Reddit

Thunder, the best Lemmy client I ever used.

Most of the apps I mentioned are free and open source and many of them are available on F-Droid. They don’t collect or sell any of your data.

The last one is not an app, but an entire OS that can replace the spyware-infested ROM that’s preinstalled by your phones’ manufacturer. I’m talking about GrapheneOS. No ads, no tracking, no proprietary Google services. Just free and open source software with maximum privacy and security. It’s so great!