Macos – Is it possible to code on two different computers simultaneously

I want to work with another programmer and I want the source code to be live in real-time on both of our screens. Is this possible on the Mac OS x or Linux? We're going to be using OS X but occasionally we might need to add an Ubuntu computer too.

Is there a way I can do this using ssh, any shell based program, or even a good GUI? I thought Coda might be capable of this but it's not really working.

Anyone ever do this? I'm not look for a git/svn/or any other version control system. This is more of a live coding session.
🙂

EDIT: To better explain this situation, let's say my friend Emily and I want to collaborate, should I have a hosted SSH over the internet?

…sometimes I find an SSH address in my sharing settings on OS X. Can I just take this SSH address and give it to Emily and will she be able to use it and after this, what do we need to connect simultaneously?

EDIT 2: Has anyone been able to do this using Coda over the internet?

Why I chose the answer that I did… Even though I found SubEthaEdit very useful, I didn't want to spend $60+ ($30 for me and $30 for my friend) on it because we already use a lot of tools for source editing. I realized that my friend is a big emacs user and I'm a vim user, also SSH was going to make it harder for myself to do the setup. Although in the future I might consider the latter the best solution.
I chose to go with DocShare because it's an add-on for a tool we both know how to use, it's free, and I feel like I will be able to work simultaneously without much trouble.

TL;DR I need a tool that helps me collaborate source code with a friend of mine, it has to be either Mac only or multiplatform. I chose to go with DocShare.