Summary.md

Known to work

System

1. eSpeak, offline TTS support for more than 100 languages

App Stores

1. F-Droid, the OpenSource app store
2. Aurora Store, googels paly store accessed anonymously

Browser

1. Fennec, firefox for mobile

Messaging

1. Signal, messaging via signal servers, encrypted
2. DeltaChat, messaging via email, auto-encrypted
3. Telegram, messaging over telegram-company servers, not encrypted, reads your contacts, not recommended

Calendar, Contacts & Files

1. Find some ideas described here: Sync your data

Navigation

1. OsmAnd, uses Open-Streetmap for offline navigation (pedestrian, cycle, car, truck ...), speech output possible.