The Simple Mobile Tools suite by Tibor Kaputa is excellent. They're all FOSS and "simple" without compromising on features. The "Pro" versions are also open source and available for free via F-Droid.<p>AntennaPod is an excellent podcast app.<p>Syncthing-Fork is superb for file sync.<p>KeepassDX is an awesome password manager<p>Signal and Element are open-source messaging apps<p>RedReader and Slide are awesome Reddit clients<p>OpenBoard is a clean, simple, privacy respecting keyboard.<p>Notally is a simple notes/to-do app that can replace the likes of Google Keep and Simplenotes.<p>StandardNotes is a superb end-to-end encrypted note-taking app.<p>Joplin is another excellent full-featured Markdown note-taking app that is offline by default but lets you use e2ee sync over Dropbox or other cloud providers.
OctoDroid - for Github
Slide for Reddit
Kiss launcher - text based launcher
Librera Pro - best eBook reader (with tts)
Antennapod - best podcast app
Termux - Linux terminal with super powers
LibGen Mobile - Sci-hub and more
Syncthing-fork - file sync that works<p>All are in F-Droid
Most of the stuff I run via Termux is open-source.<p>(FWIW, Termux on an Amazon Kindle Fire HD 10 is really nice; I got mine via on sale for about $100.)