It's the script file for canmttale! This is the best way to handle the editing process over multiple different writers.
To make a change, click into the script file and hit the "edit" button. From there, make whatever changes you want.
When you're done, write a short paragraph describing what you changed, and select the "Create a new branch" option.
This gives everyone else an opportunity to review what you wrote before it gets saved to the main file.