Everyone knows the popular ones so here's a shout out to a few that are perhaps not so commonly known:

• whoBIRD - Shazam for birds
• Subz - Subscription manager
• zCard - Loyalty/membership/store card wallet

My most used can no longer live without app:

• Joplin - Note taking. Various sync options. Brilliant app, helpful community & very regular updates (especially desktop)

Tubular. It's a fork of newpipe incorporating sponsorblock and youtube dislike.