Do I need to pre purchase tickets from Stuttgart to Eislingen and Stuttgart to FRA (airport) for early Dec, and what app should I have? Thanks travelers!
To FRA, yes. To Esslingen, no. Local transportation within the VVS zone of authority will handle the Esslingen trip. Ride only local and regional trains:
Saver fare tickets on long-distance trains can be had at DB 1st or 2nd class:
https://reiseauskunft.bahn.de/bin/query.exe/en
The DB app should give you access to both ticket types.