Some useful links

1. New York Film Academy : Student Resources
2. How to Write a Documentary Script, A Monograph by Trisha Das  [Published by Unesco]
3. Georgetown University : documentary script format
4. BBC Writers’ Lab

Open-source writing software

Trelby [Linux, Windows]

Celtx [Final Draft alternative, payment required]

Fountain, creating rules for writing screenplay in plain text.

Video collaboration

Frame io.