Mozilla's Bespin, released today, is a cloud based development environment that acts as a collaborative working space. This has HTML5 Canvas, runs the tools in the cloud and pretty response - see the screen capture that I posted here.
There is a very decent editor on the hosted & extensible dev environment. There is also an integrated CLI, emacs and collaboration features.
What is missing are the publishing, caching capbilities, ability to do version control, client-side customizations and the standards enforcements. Hence - but this is just version 0.1
