My daily sojourn to the coffee shop to work on my feature screenplay -- of which I'm happy to report I've just completed a third draft -- is often accompanied by the sight of other folks working on their own script. I live in Williamsburg, Brooklyn, which is probably the Aspiring Screenwriter capital of New York, so it's a common sight. But I've been surprised recently at the number of times I'm seeing Celtx instead of Final Draft -- probably due to the fact that the former is free. On the desktop, that is: the mobile version is $9.99, and just went version 2.0.
The iOS app, which works on both iPhones and iPads, now features page breaks and page numbering, scene re-ordering, colored notes, pinch-to-zoom, and a number of other new features. Hit the image below if you're interested in writing on the go (well, even more on the go than a laptop):
Link: Celtx for iOS