My "Top" apps are what I think are cool, not necessary what the most useful apps are to me.

Briar its a peer to peer communications app that can communicate via wifi, blutooth, or through the internet via Tor. It can form a sort of mesh network with devices in proximity. Hypothetically, with enough users, you could spread information across a long distsnce even with a nationwide shutdown of the internet like some authoritarian countries do.

There's already some public forums on there by connecting to random people around the world via Tor, although, these forums doesn't have much activity now. But it exists and thats so cool. Its like a secret corner of the internet, even more obscure than the "dark web"

Wasted Remember those news about iPhones randomly restarting in police storage lockers? This app does something even better. Amongst many functions, this app can let you set your phone to auto-wipe itself if not unlocked for X amount of time, ranging from 5 minutes to 7 days. (Warning: You may get in legal trouble for using this, if you get arrested and the phone auto-wipes, you could get a "Destruction of Evidence" charge. I am not a lawyer. You might wanna consult a lawyer before using this)

OpenKeychain Just a PGP tool for Android, pretty straightforward. Very cool to have a digital signature right in your pocket to validate your online identity with other internet users. Potentially useful for ~~secret drug trades~~ ahem just kidding lol, don't do drugs, kids. (Seriously, don't)