Zotero is an excellent tool for managing a database of references. My usage so far happens to be no-frills -- just a collection of articles including their PDF versions, mostly of arXiv. I have been using the 500MB free storage that is freely available on Zotero servers, but now I've used up that space. Instead of paying Zotero for extra cloud space, I decided to use UTbox. The service allows access via WebDAV and is quite easy to set up. Since WebDAV is a standard protocol, the same procedure must apply for any hosting service with WebDAV access . WebDav access for Dropbox seems conspicuously absent but they seem to be focusing more on creating a seamless native experience on most platforms. There are third-party solution providers who offer WebDAV access to Dropbox for a price.