From official F-Droid & IzzyOnDroid repos (except for Molly):

1. Aegis Secure + encrypted 2FA

2. Calculator++ Powerful scientific calculator

3. Clipious or FreeTube Android Clipious: Privacy focused invidious client that syncs with your account and lets you pick backup instances in case yours goes down FreeTube: Ad-blocking cross-platform privacy-focused YouTube client that imo looks better than NewPipe + Clipious

4. FluffyChat (if you use Matrix) Secure, private (although not as good as Signal), client for Matrix (the messaging service) that imo looks better than Element and lets you seperate rooms + DMs, which some clients don't let you do iirc as well as a couple other features like pinned messages and video calls.

5. HeliBoard Best open source keyboard I've used so far

6. KeePassDX KeePass compatible password manager

7. Moshidon and/or Mastify Mastodon clients. Mastify looks really good but is till in Alpha releases so is missing quite a bit of features. Moshidon is extremely feature rich.

8. Molly Security-focused fork of Signal

9. Podverse My personal favourite podcast app, run by 1 person afaik with a lot of free features, or a very cheap paid plan that is basically just a donation because it only adds like 2 features that I can remember. Has a very generous trial too and the dev has said if you can't afford it they're willing to adjust pricing for you.

10. QUIK SMS Best actively maintained, open source SMS client.

11. Twine Beautiful cross-platform RSS feed app.