Pixelapse comes pretty close.
Here's what they offer:
- Public gallery
- Downloadable source (e.g., PSD, AI, etc.)
- Revision history
- Commenting and annotations
- Dropbox-like saving behavior
Here's what they don't have:
- Licensing information for public works
- Explicit "fork" behavior and "pull" requests
Here's a sample I added to try it out: www.pixelapse.com/artworks/92981-store