I was researching this and came across a number of issues -
- owncloud app doesn’t work with sandstorm.io’s davros (I don’t want to run owncloud)
- play store reviews saying seafile can’t sync folders
- syncopoli needing to download binaries to be functional
- syncthing not supporting external storage
- git-annex not working on recent versions of android because it uses “text relocations”.
What do you use and why?