Mendeley has this feature too. Their current desktop uses Qt. One of the other things going for Mendeley is seamless sync between an iPad and a desktop. Their

Mendeley has this feature too. Their current desktop uses Qt. One of the other things going for Mendeley is seamless sync between an iPad and a desktop. Their cloud limit is 2GB free storage. Though Zotero has Zotfile, it’s a hassle to set up tablet sync with an iOS device.