Bespin

Mozilla's Bespin is an interface through which web developers can work together on the same project from different machines in different locations. It supports HTML, Java, and CSS, and it stores the code for each group's project in the cloud, allowing any of the group's registered users to access and edit the code using any web browser, on any computer, from any location. At least, that's the goal; the Bespin project is still in development (likely a collaborative development, at that).