PeerLock Server adds File Locking to MS DFS, it can prevent users from modifying files that are currently in use or that are being changed by any other users.
PeerLock Server allows access to those files based on Source File. Other features include support for UNC folder or path names, cross domain locking, and the ability to manipulate the locked list of files.

How It Works
When a user opens a file in a watched folder, the corresponding target file is immediately locked on the other machines specified in the user selection list. Other users cannot make modifications to this file. When the user closes the file, the files residing on the other machines are immediately unlocked, and can now be used to make changes. PeerLock is designed to work with our PeerSync and Save-N-Sync products as to offer a total locking and synchronization solution.

Limitations:
* Limited functionality

The license of this software is Free Trial Software, the price is $1399.00, you can free download and get a free trial.