Tools
APPS: App Manager (f-Droid)(Root) (Easy disable/Uninstall apps incl. default apps)
Battery: Battery Charge Limit (F-Droid)(Root) (extend battery life)
Note App: Carnet (F-Droid)
QRcode: QR-Barcode Scanner (F-Droid)
File Manager: Material Files (F-Droid)
Travel
Bahn: DB Navigator (Aurora) (Must have if you want to buy a ticket last minute)
Local: Öffi (F-Droid)
Picture/Video/Audio
Gallery: Simple Gallery (F-Droid)
Camera: Open Camera (F-Droid)
Music: PoweAmp (Direct von Dev)
Contact
Messenger: Signal (Aurora)
Video Messenger: Jitsi Meet (F-Droid)
Mail: K-9 Mail (F-Droid)
VoIP: Linphone (F-Droid)
Sync/Backup
CalDav/CardDav: DAVx5 (F-Droid)
Calendar: aCalendar+ (Aurora)
Tasks: ToDo List (F-Droid)
Backup: SMSBackup+ (F-Droid) (SMS send as E-Mail)
Sync Tool: Syncthing (F-Droid)(Syn with PC and NAS)
Finance
Manager: Subz (F-Droid) (Manage expenses and keep an eye on finances)
Social+Media
Radio: Transistor (F-Droid)
Reddit: Infinity (F-Droid)
Youtube: New Pipe (F-Droid)
Mastodon: Fedilab Lite (F-Droid)
Brwoser: Fennec (F-Droid) (With AddOns)
Twitter: Fritter (F-Droid) (Without Twitter account 
)
Protect
Call blocker: Yet Another Callblocker (F-Droid)
Tracker block: Warden (F-Droid)(Root)
Malware: Hypatia (F-Droid) (Paranoia 
)
Redirect: Untrackme Lite (F-Droid)(set post deleted by default to open Twitter, YouTube and Instagram links will transform them into Nitter, Invidious and Bibliogram links. Usefull if get a Twitter/Youtube/Instagram link via messengerauthor)
Extras
Root: Magisk (GitHub) (Need for some must have apps)
Router: MyFritz App (Aurora)
VPN: VPNcilla+ (Aurora) (Special need for FritzBox Router)
Automation: Tasker (Direct from Dev.) (Root) (e.g: Wi-Fi On/Off, Display Rotate, AOD, Notification/Ring mute base of calender event…)