CS Music: formerly Cesium: iOS’s music app used to be really good. No more. Hence.
Overcast: iOS’ podcasts app used to be the best. Again, no more
Readder: Main, fun Reddit account
Apollo: Account with fewer, more focused subscriptions
Blockquote: plaintext editor with great iCloud Drive support
Files: files app with great iCloud Drive support
Sheets: personal and work spreadsheets. Many populated by IFTTT recipes
Health: tracking water intake (populated by an iOS Shortcut), meditation (“Mindful Minutes”, also populated by Shortcut), heart rate (populated by Soul Solver via a Fitbit).
Evernote: research material for projects
Microsoft Todo: main todo app. Does lists better than iOS Reminders
Launch Centre Pro: Launches apps and Shortcuts manually but based on time and geofencing. I use it multiple times every day and almost feels part of the OS.