Celtx for AV
Celtx added an AV editor in version 0.99.5. Working in conjunction with the Typeset feature, the AV editor provides a simple, screenplay-like editing environment that uses Typeset to generate an industry standard two column shot format.
The writing process is very similar to writing a screenplay, with the <Ret> and <Tab> keys providing easy navigation from one element (eg. Scene Heading) to another (eg. Action). You can also use the element drop down menu to change any element.
Source(s): AV editor solutions
This is what a script looks like in the editor:
And this is the same script after using Typeset: