Sign up for an account at Scripped. This is a free online screenwriting software that features all the tools necessary to write movie scripts. The only requirement is that you sign up for an account. Once you sign in, typing your script is as simple as hitting TAB and ENTER. You can also manage your screenplays online. Scripped is entirely Web-based and requires you to download nothing to your computer. Scripped allows you to save your screenplays as PDF files and save them to your computer so you can market them.
Use Plotbot if you want to write a screenplay with a partner. Plotbot is a free screenwriting service that allows you to connect with your writing partner and collaborate in real time. The only requirement for Plotbot is that you sign up for an account. The changes you and your writing partner make are tracked and saved to both versions of the screenplay.
Consider using Scriptbuddy to write your screenplays and share them with an online community that will review your scripts and offer advice. Scriptbuddy offers free scriptwriting tools and writing-community support. This is a good choice for writers who wish to get outside opinions about the quality of their screenplays.
Download and install Celtx if you prefer to have a screenwriting program on your computer but like the idea of online storage and a writing community. Celtx is a free full-featured screenwriting software that is partially Web based. You do need a connection to the Internet to use Celtx, which allows you to back up your scripts online, save projects and communicate with writing partners.