Ask HN: What's the best setup for remote pair coding in your opinion? (Rails)

Title mostly says it all. I'm trying to get myself up to speed to build a pretty complex rails app from scratch, something I've never done before. I've hired someone to help me, we'll check in every day and share a screen and and talk over the project and I'll get pointers and learn stuff while we work on the same live code together. I've considered something like Cloud9 to host the development instance, deploying to Heroku for production. But Cloud9 is a little clunky of course so wondering if there's other options people like for live collaboration on actual code, Google Docs style where you're really doing it in real time.