Seafile is a file synchronization and collaboration platform. It comes with Dropbox-like file syncing, but is designed to be better suited to teamwork. You can build a file syncing and collaboration service for your team on your servers. It can also be used to build your own Dropbox for personal use.
Kune is a distributed social network focused on collaboration rather than just on communication. It focuses on online real-time collaborative editing (Wave-based), decentralized social networking (federation), and Web publishing, while focusing on workgroups rather than just on individuals. It aims to create online spaces for collaborative work where organizations and individuals can build projects online, coordinate common agendas, set up virtual meetings, publish on the Web, and join organizations with similar interests. It has a special focus on Free Culture and social movements needs.