Applications :: Finding Project Management Software?

I work for a theatre company. We want a software package that enables us to manage our production process over distances/online: playwright in one place, director in another, designer somewhere else, etc. These are small project teams, so we don't need anything vast, but the package does need to be able to respond to different project structures and styles and feel intuitive.

I've looked at Things and Project X online, but can't seem to get a definitive view about about how easily (if at all) they enable people to collaborate online (that is not on a local network).