Keyboard:

• AnySoftKeyboard good all around keyboard, good language support, decent though messy customizability
• Unexpected keyboard more specialized, provides easy access to app (printable) ASCII characters and some others, allrght customizability
• 8Vim Cool factor, great customizability, decent language support but you need to learn it

Games:

• Pirate Solitare nothing much but I've been playing it a lot lately
• Simon Tathman's Puzzle Collection a cross platform puzzle collection, has a lot of different puzzles in a uniform style
• Antimine minesweeper with nice ui

System:

• RethinkDNS: DoH provider and firewall Easy to use, especially nice for those non FOSS apps you need to have to maintain a social life, not that powerful though
• Obtainium: FOSS app downloader Downloads apps from releases or equivalent, therefore can have faster updates than fdroid, but no discovery, aside from search on some platforms
• ffupdater: FOSS browser downloader Like obtainium, but for browsers (mostly) and has list of browsers
• Droid-ify: fdroid client better ui than the default app, comes with a list of repos
• Shizuku: ADB shell api not useful if you have root (see SUI, which is the root implementation for the same api, though shizuku will also work I think), but can give a bit more access if you don't supports wireless debugging on A12+
• Neolauncher: launcher nice ui but nothing special
• SD Maid SE: storage cleaner okish ui, doesn't stop me from having 302 (not including system) apps on my device. Yes I have a problem
• Package manager: app manager Shizuku support, powerful, though limited if you don't have root
• Inure: app manager [freemium (8$), but GPL licensed?] pretty must like Package manager but with amazing ui

Media:

• LibreTube: Piped (youtube) client Nice ui, no ads, sponsor block support, kinda unstable
• Innertube: YouTube music client doesn't use piped/invidious, no ads, nice ui
• Tusky: mastodon client nice ui, quite stable, multiuser support
• Jerboa: lemmy client ok ui, up to date with lemmy updates
• Liftoff: lemmy client nicer ui then Jerboa but doesn't work since .15 (?) and had issues with rendering markdown properly
• LibreTorrent bitTorrent client for downloading all those isos and public domain works, nice ui

Misc:

• Mull: ff based browser not much to say, "security oriented and deblobbed", upstreams some features from Tor
• Calculator++: A scientific calculator A lot of functionality while remaining easy to use
• RPNcalc: A Reverse Polish Notation calculator best RPN calculator I've found on fdroid, less powerful than Calculator++, but RPN based calculators are more efficient^[citation needed]^
• Simple Apps: suit of apps providing basic functionality great ui and customizability, I don't use simple keyboard, simple launcher/drawer however
• OpenCamera: a camera app advanced features

Just the apps I thought of, as I, as mentioned in the SD Maid entry, have a lot of apps installed :P