Most of those apps are available on F-Droid, F-Droid repos or other sources.
- AuroraStore.apk: Opensource Google Play-Store client with nice features and a better design. Can be updated using their website or Telegram.
- Bromite.apk: Chromium based Webbrowser with ad-blocker and privacy tweaks. Can be updated using their github page (this script uses arm_ChromePublic.apk) or their F-Droid Repo.
- F-Droid.apk: Appstore full with opensource apps. Can be updated using F-Droid.
- K9Mail.apk: Opensource E-Mail app using POP3/IMAP. Can be updated using F-Droid.
- MaterialFiles.apk: Opensource material design file-manager. Can be updated using F-Droid.
- Metro.apk: Opensource music player based on RetroMusic with all premium features. Can be updated using F-Droid.
- NewPipe.apk: Opensource YouTube app with extra features like PiP, background player, music/video download, local playlist and subscribers without using proprietary Google-APIs. Can be updated using their github page or their F-Droid Repo.
- OpenBoard.apk: Opensource keyboard app based on AOSP Keyboard with more features, themes and some improvements. Can be updated using F-Droid.
- QKSMS.apk: Opensource SMS app with nice features and customizations. Can be updated using F-Droid.
- SimpleGallery.apk: Opensource gallery app with nice customizations and features. Can be updated using F-Droid.