Huh? I’ve seen zero implementations that work seamlessly across computer, phone, tablet - unless they are all single platform, which I have yet to see anyone actually pull off.
I can't speak for other platforms; I stopped helping ${EXTENDED_FAMILY} with non-Apple questions because the crap I had to diagnose, debug and deal with for Windows and Android was worse than ${DAY_JOB}.
All sync seamlessly and support the major (and often minor) browsers.