Vita is an web-based vi clone that aims to provide a reasonable in-browser experience, especially on devices that don't have arrow keys like the iPhone.
Vita is implemented on top of the HTML textarea. This differs from related projects (like jsvi) in that it only requires a textarea and JavaScript, so it works in very limited environment.
It's very early in development, but does allow some basic text editing even now. Essentially, I'm developing the features I find that I need, but if you're interested in helping out, drop me a line at hello@benjaminoakes.com or via Twitter at @benjaminoakes.