I just put my Calibre library in Dropbox and get apps like Calibre Sync for Android. It integrates with Dropbox, downloads the library metadata on demand, and l

I just put my Calibre library in Dropbox and get apps like Calibre Sync for Android. It integrates with Dropbox, downloads the library metadata on demand, and lets you download the books you are actually reading. I combine this with sorting by recently modified/custom Calibre columns for managing what is Todo or various 'shelves'. It lets you make a custom 'tag' column.