Seafile is a next-generation open source cloud storage system with advanced support for file syncing, privacy protection and teamwork.
Collections of files are called libraries, and each library can be synced separately. A library can be encrypted with a user chosen password. This password is not stored on the server, so even the server admin cannot view a file's contents.
Seafile allows users to create groups with file syncing, wiki, and discussion to enable easy collaboration around documents within a team.