F-Droid Basic is cool. Same thing, just without some sharing options etc., you probably don't use anyway. It was the first one to get actual background updates on modern android.
Barcode Scanner is decent, it even searches for products online, if you scan something that looks like a food label etc.
Casio G-Shock Smart Sync if you are tired of official Casio app in a casio bluetooth watch.
DuckDuckGo is there...
FadCam - if you ever need a recording without tracking attention (while phone is locked). Could get you out of some legal trouble...
Futo Keyboard is interesting project.
GadgetBridge saves some old devices. I use it for some Xiaomi eink devices that overwise require... to be connected to chinese datacenter to be discovered and sync. Which is insane, as some versions discover and can be synced on EU servers...
Grayjay for videos on many platforms.
So many HackerNews clients - I'm on Hacki currently.
Home assistant, Jellyfin, Joplin, Mullvad, Telegram, Nextcloud, Organic Maps, Osmand~, Tailscale or Yubico authenticator are all there. I like them better from f-droid.
Street Complete is an awesome way to contribute to OpenStreetMap.
Thunderbird (!) which is a fork of K9 (still active), and looks and runs great. Highly recommend.