Free and Open Source Software
If it's free and open source and it's also software, it can be discussed here. Subcommunity of Technology.
This community's icon was made by Aaron Schneider, under the CC-BY-NC-SA 4.0 license.
On my Android tablet, my most used app has got to be either Mull (web browser, based on Firefox), NewPipe (YouTube client), or Tusky (Mastodon client).
My favourite app, however, is probably UntrackMe.
Right now, Infinity for Reddit, but with the Reddit API debacle, I guess it's either Jerboa for Lemmy or Firefox Focus.
Favorite would probably be either Material Files file explorer or K9 or Proton Mail for email.
Simple Gallery (and the Simple Mobile apps in general), AdAway, SDMaid, Magisk, Firefox.
Revanced for YouTube, Audacity, KDENlive, VLC, OBS studio, and the *ARR suite of applications.
Edit: I did not see that you said Android. Revanced it is then.
vlc has an android app too! try it out !
Revanced isn't open source. the patches are, but the base client is closed.
Nextcloud Notes for notes