Excellent. Does precisely what it says, and does it beautifully. Great for getting the stuff down (though eventually it'll need -- probably -- to go through one of the prehistoric Cruft Machines like Final Draft or MMScreenwriter) and the intelligent formatting of plaintext means, surprisingly, an end to all that old stuff about "Why the hell are all these Action elements being formatted as Dialogue?" and tedious reformatting. And it does stage play format. AND lyrics. Hurrah.
The only thing is, there's not so much steampunky fun in formats and revisions and so on that you get with the oldsters. If you're doing this for a living, that's good. If you're doing this for a hobby or because you want to write screenplays/stage plays one day (this is emphatically NOT a sneer) you won't feel quite so... not sure what the word is... "validated", I suppose. You know; "I'm using Final Draft so at least I'm using the same software as [insert name of hero writer]". We've all been there, and it's comforting. But for actual work, with someone scowling outside the door, tapping their foot and drumming their fingers, this is a Good Thing.
(And the Melting PDFs feature is *really* cool.)