J. R. Haigh's recommendations for Android
F-Droid (https://f-droid.org/ ) – libre software repository, from which the following can be downloaded (GPLv3+) (To install, you need to enable ‘unknown sources’ because it is separate from Google.);
- FAST App Search Tool – quick application launcher from double-clicking or up-swiping the home button (GPLv3);
- Hanger – recent application launcher widget for notification bar (tip: pin FAST so that you can quickly get to applications that have fallen off the list) (GPLv3);
- Kiwix – offline Wiktionary, Wikipedia, etc. (GPLv3);
LibreTorrent – reliably download large files such as those used by Kiwix (GPLv3);
- RPN – step-by-step calculator with no need for parentheses (e.g. compare 1, Enter, 2, Enter, 3, ×, + with 1, Enter, 2, +, 3, ×) (GPLv3+);
- Open Camera – advanced still and video camera (GPLv3+);
- MuPDF – view portable documents (PDFs) often attached to emails or downloaded (AGPLv3+);
- VLC – media player (GPLv3);
LeafPic – media gallery (GPLv3);
- Hashr – verify files (GPLv3+);
- Amaze – file manager (GPLv3);
- Ghost Commander – advanced file manager (GPLv3);
- Turbo Editor – text editor (GPLv3+);
- Lock Screen – in combination with unchecking the ‘Power button instantly locks’ security setting, this is a partial workaround for Android not distinguishing between locking the screen and locking for security (GPLv3+);
SatStat – sensor status with ability to manually or automatically update AGPS data for quicker positioning fix (GPLv3+);
- Transportr – public transport planner (GPLv3+);
- Suntimes – show, and set alarms for, sunset, twilight times, sunrise, and noon (GPLv3+);
- React – test your reaction time (GPLv3+);
- Periodic Table – chemical element browser (GPLv3);
- Quill – draw visual notes, especially with stylus (lacks handwriting recognition) (GPLv3);
- Flym – feed reader, supports RSS and Atom feeds (GPLv3);
WiFi Analyzer – analyses Wi-Fi channels (GPLv3);
- Rotation Manager – set application-specific orientations, a workaround for some Android rotation issues (GPLv3);
OsmAnd – offline OpenStreetMap (GPLv3);
NewPipe – YouTube downloader for later offline playing (GPLv3+);
- Mitzuli – offline translator (GPLv2+);
- Barcode Scanner (search ‘zxing’) – scan barcodes and share via QR codes (Apache2);
- K-9 Mail – email client (Apache2);
LibreOffice Viewer – view office documents (MPL2);
IceCat Mobile – Web browser (MPL2);
Activity Launcher – create homescreen shortcuts directly to specific activities within applications, such as the ‘Tethering & portable hotspot’ activity within Settings (ISC).
All of these applications are libre software (you are free to use, study, modify, and share them) and the offline content files for OpenStreetMap and Wikimedia's wikis are also libre.