Originally Posted by Philantrop
iBooks, Kindle and Kobo support that, provided you download the ebook(s) on all devices you're using.
Just to be clear:"devices" doesn't include a Mac, which is the topic of this thread...
But one thing before we get back on topic - Kindle does automatically sync reading position, bookmarks, and highlights, between iOS and Kindle devices, via wifi and cell networks. Sometimes it takes a while though, in my experience.