There's been a lot of discussion about how we need github-like features on d.org. Will we get them? There's definitely many improvements in the pipeline to the way our issue queues work. Whether we actually need to replicate github is another debate (and my take on it is that I don't think we do).
In the meantime, I think that it's possible to have a good collaborative workflow with what we have right now on drupal.org, with just the issue queue and patches, and git local branches. Here's what I've gradually refined over the years. It's fast, it helps you keep track of things, and it makes the most of git's strengths.