So almost everything is text (with markup/markdown) and can thus easily be synced and merged between devices via rsync, ssh and perl or shell scripts.
Example: when I want to look up notes in either markor's or diary's files, that's easily accomplished with a shell script, e.g.
cd ~/storage/shared/Documents/markor
if [[ $# == 0 ]] ; then
exec zsh
else
grep -i "$@" **/*(.) | less
fi
Instead of grep I could even use agrep to handle typos. I can start a simple web server on the phone or tablet, if needed: python -m http.server $PORT --bind 0.0.0.0
and view media files from another device (mobile, desktop, laptop, … whatever.And there's exiftool, ffmpeg, ImageMagick, scripting languages, all in reach, wherever I go.