Can Syncplicity be used with others users to collaborate on files?

That's actually one of the strong points of Syncplicity! If you use Syncplicity in your organization and you would like to share with someone outside your organization, you do not need to worry about the other user having a Syncplicity account or not.

Syncplicity will create a FREE Personal Edition account for the external participant if you e.g. want to share a folder with that person.

here is a video that explains it: https://www.youtube.com/watch?v=G4Vim3-xDe8