Parallel Word Processing is a term used for collaborating on the same document in "real time". Now, there are applications that do something very similar the most popular being Google Doc's, but in reality that is not done in "real time". The two I'm very excited about our Text Flow and Ether Pad.
Text Flow - This is true Parallel Word Processing. Upload as many documents as you like and then collaborate to get your desired result. It really is a time saver and helps eliminate mistakes. View the demo here.
Ether Pad - is great due to it's simplicity in use. All you have to do is click on Create New Pad, share the URL, and then start collaborating. While it may not have as many "bells & whistles" as some other apps it certainly gets the job done. For a demo click here.