Attached Link: http://www.rsalsbury.co.uk/rd.htm

I think if all you are looking for is a way to do formatting, then there are software packages to do that, but they are not going to do the work for you of creating a dramatic structure for your play. Some of the problems you are experiencing...differentiating between the speakers...has to do with something you have to work on yourself. Who are these people? What is their background? How did they come to be on the stage together? Why are they in conflict? And they better be in conflict, or it will be a boring play. What is their relationship to each other? Are they strangers? Related? Friends? Lovers? Answer the age old questions of who, what, where and how in relationship to the characters and their problem. I don't think writing a play should be seen as being easier than writing a novel. A play has its own challenges. Any word processing program, by the way, can open two windows at the same time so you can compare versions. Here is an almost free software that might help. It's called RoughDraft. Never used it. The description sounds close to something that might help you: "RoughDraft is a freeware word processor. Although suitable for general use, it has features specifically designed for writers of novels, short stories, articles, poetry, plays and screenplays. It's designed to be as practical as possible, offering all the features you need, but without being complicated or awkward to use."