Celtx is a free, open source software tool for writing and formatting a screenplay to meet the exacting screenplay submission standards set by the theater and film industries.
Celtx permits the author to include photos, video, and audio in their screenplay. It also provides features for collaborating with other authors.
Celtx runs on Macintosh, Windows, and GNU/Linux computers, and was built using the Mozilla Firefox source code as a codebase.