Coviz is a tool that uses visualization to support spontaneous construction, organization and exploration of collections. We use the term collection to identify a set of documents gathered for a given purpose by one or several individuals. Coviz facilitates creation, organization and update of collections by providing multi-scale visualization and interaction techniques. Coviz has been tested in several informative case studies involving small groups of users. In these situations, Coviz has fulfilled several important aspects of both groups and personal organization needs. Our initial experiments indicate that Coviz can even encourage unusual and interesting forms of cooperation among people.