Full user review
"Great tool for writers"
It's free and it does what most other screenplay software applications do
The only "con" with this software is the strange difference between the "non-formatted" editor (which you use to do all of your writing) and the "formatted" screen (which takes a few seconds each time you click on it, to formally format your writings)
I have not yet had any issues with Celtx -- seems pretty stable and reliable. Would recommend screenwriters try it before spending money on a similar tool