Chatbox is a free Mac OS X application that brings simple project collaboration features into Dropbox.

It allows us to comment to files hosted on Dropbox and easily start a discussion/chat about them.

Once installed, right click any file/folder and instantly start conversations with the people that the Dropbox file/folder is shared.

It can work offline, syncs when you are back online and requires no registration as everything is stored inside Dropbox.

Chatbox for Dropbox