Hyphen uses iCloud (and I think it gives you the option to sync only annotations, or entire books along with annotations).
For MapleRead, you create your own "MaplePop" user account, whatever that is.
And that, apparently, allows you to sync annotations.
And, in both, you can email your annotations to anyone, just like from Marvin.
I haven't tested Hyphen or MapleRead in terms of annotations syncing so far, because for the time being, Marvin remains my "daily driver" e-reader, so I continue doing this manually for now. That is, by exporting annotations from Marvin manually, via HTML, from all of my iPhone/iPad devices, then manually checking and fixing
all the corruption errors mentioned above, in the HTML files, and finally arriving at a "clean" annotations list by manually merging the HTML annotation files from all devices. (I use the SeaMonkey Composer for the manual merge, although Word or LibreOffice would likely accomplish it as well.)
By the way, that bug/corruption I mentioned occurs, at least in Marvin (but perhaps in the other two as well), not just for the highlights quoted from the book texts, but for
user-written annotations, it happens as well: all paragraphs in a user-authored annotation get merged into a single paragraph (meaning, all line breaks get deleted). That's doubly inexcusable... This corruption of highlights/annotations upon export simply needs to stop, if any of the three e-readers – Marvin, MapleRead, or Hyphen – seriously wish to call themselves "top-quality e-reader software" one day.
