PhantomJS now includes the GhostDriver project.
You are also suggested to use PhantomJS directly or with a convenience library such as CasperJS. CasperJS is specifically designed to make it easy to do sequential operations to web pages, perfect for many automation tasks.
Disclaimer: I am the author of PhantomJS.
Edit: As noted in Nick’s answer, GhostDriver is now included in PhantomJS.