IconJar allows you to move your Library to any location. This does allow you to move your Library to a Dropbox folder or similar alternatives.
That being said, there are caveats. IconJar was never built with sync in mind and thus there are certain precautions. The main one being avoid using IconJar simultaneously across different Macs. Always wait for sync to finish on one, close the application and then open on another machine once the syncing has finished.