Use Zotero at multiple computers with syncing. Library items are synced through the Zotero servers (unlimited storage), while attachment syncing can use the Zotero servers or your own WebDAV service to sync files such as PDFs, images or audio/video.
Zotero users can create collaborative or interest groups. Shared group libraries make it possible to collaboratively manage research sources and materials, both online and through the Zotero client. Zotero.org can be the hub of all your project group's research, communication and organization.