DropBoxWatcher for Mac

From MotaSoft Software:

Drop Box Watcher, also known as DBW for simplicity, watches your Drop Box (as well as most any other folder on your network), and alerts you when there's a change. Never lose a document again. Watch some of the more critical folders on your computer to catch would-be criminals. Sharing files with friends? Be alerted when they give you a new one. Also offers robust filters to disregard changes you don't want to know about.