This is something that I am loving right now. It's a handy writer's tool called Writeboard. Writeboard is part of a larger program that I often use when working as a freelance copywriter with clients, called Basecamp. These are software programs that create a place for you and your collaborators to work together in cyberspace. You can dialogue back and forth, upload documents, make to-do lists and set time lines and goals that have built in reminders, to one another. You can mark up each others documents, you can log on and work anytime of the day, and you can keep it organized all in one neat space. I love it, because it is so organized, and it keeps things professional. There is no need to write an email every time I have a question, and if an idea comes to me later, I can simply add on to it, without resending the entire document. I also love that I don't have to pester anyone about looking at my work. Basecamp will send an email to all involved letting them know that changes have been made and to go and see them.
If you are someone who works online a lot or who collaborates, I can't recommend this program enough. And no, I didn't get paid to advertise it, it just makes my life so much easier, and anything that makes writing easier, I have to share!