No invite yet, but from what I see from their blog (http://blog.koding.com) Koding seems to offer all kinds of collaboration-coding tools via your web browser (for free). Version control springs to mind, as does my code trusted to the "cloud".
I've been using this for around 8 months. It's one of those apps you wonder how you managed without it. It's keyboard-based note-taking, with search and integration with Simplenote. It's a fork of Notational Velocity.