http://www.finaldraft.com Final Draft is the screenwriting software most used by screenwriters and independent filmmakers alike. Made to run on MacOS and Windows, Final Draft is exactly the same for both platforms.
Final Draft easily imports your work from any word processor without you needing to edit or format it in any way. Over 50 templates for television, movies, and stageplays are included with locations and characters. Along with this, collabowriter allows you to work with another person on your script in real time over the internet.
A built in format assistant will check over your script and look for common formatting mistakes. Write in another language? Final Draft also includes dictionaries and thesauruses for 17 languages. ScriptNotes is a helpfull little in-program that lets you jot down ideas and keep them organized without messing up your script.
And the Text to Speech feature is really great and usefull. It allows you to assign different voices to each character and the narrator while it reads your script out to you.
If you are looking for something better than a word processor and are willing to spend some money, then Final Draft looks to be a very good program to use. Also, depending on what site you go to there are student discounts available.