Seafile (http://seafile.com) is an open source file synchronization tool.
It comes with Dropbox-like file syncing, but is designed to be better suited to teamwork.
You can build a file sharing and syncing service for your team on your servers.
It comes with many interesting features:
1) Users can create and join groups, then share files to the group. This makes it convenient for teamwork.
2) Files are organized into libraries, each be selectively synced to your computer. Libraries can be synced with any local folders.
3) Online file collaboration features, such as PDF and Office file preview and file commenting.
The project is hosted on Github (https://github.com/haiwen/seafile).
Compared to earlier open-source projects, such as SparkleShare and ownCloud, Seafile has several advantages:
1) Production quality file syncing algorithm.
2) Many team collaboration features.
The client-side software now runs on Windows, Mac OS X and Linux. And server-side runs on Linux.
The 1.3 release comes with many improvements:
* Encrypted data transfer
* Server-side garbage collection
* UI improvement for online markdown/text file editing