Notepad Free. Exactly what it says. No more, no less. No ads.

Exodus scans your installed apps and tells you which ones require ridiculous permissions and trackers. You should download it after you try the other apps on this thread to make sure you're not using anything that's basically spyware.

LMT. I just can't do without my pie menu—saves me screen real estate and it serves me much better than whatever built-in gestures my devices provide.

Unlauncher changed my life and helped me break my addiction to my phone by using monochrome home screen with no icons so I didn't get dopamine hits when I looked at my screen to open an app.

Tasker is wonderful for automating tasks

KLWP is great if you want to go full custom with your Homescreen and Lockscreen, allowing you to generate custom interactive live wallpapers which can act as a dashboard or as a launcher

For anyone who lives in Houston Texas or the surrounding area, Space City Weather is a phenomenal no bullshit, no ads, just weather app.

Not sure the popularity, but here's what are essential to me:

AnySoftKeyboard - a custom keyboard that supports layouts like workman/colemak

Simple Gallery - Fantastic gallery app

Mule - Secure version of Firefox

OneTracker - simple bullshit free parcel tracker

Xplore - dual pane file manager, been using it for over 10 years. Can't go back to regular ones

Yubico Authenticator - Used to get OTPs off my Yubikey.

I have more essential apps, but they'd fall close or in popular.

Keepass Syncthing