Keep an eye on this one. It's growing fast, and becoming more and more powerful. Mozilla Bespin is a project to create a full, textmate style text editor inside your web browser. Recent additions to the code include multiuser editing/collaboration, and more importantly, subversion/git controls. It includes preview/run functions for HTML/javascript, and is quite stable now.
One interesting feature is they plan to integrate it with sites like sourceforge.net and github, thereby making the process of checking out and making changes happen completely in the browser. Couple this power with a tablet like the promised Apple wonder or the Crunchpad, and you've got a winning combination for coding on the go.
In the past, when I've had to work on sites on the go, I've often ftp'd in through someone else's computer terminal app, ssh'd to my server and edited the files on emacs or vi. Maybe now I'll just boot up a browser.
