Right now the only option is nano/vi in the shell - and these suck for beginners.

Best current option is: http://github.com/zefhemel/zed/

which is geared towards a chrome app for packaging, but will work as regular html/js

Some notes on running it outside of chrome app:

editor.html is the main vehicle

To start up in regular chrome mode:

open chrome with same origin disabled:
open -a '/Applications/Google Chrome.app' --args --disable-web-security

switch to zed/app and then:
python -m SimpleHTTPServer 9999

in another terminal open zed/server and then:
python webfs.py

in chrome open:
http://localhost:9999/editor.html?url=http://localhost:1338/tmp/zedproject

will open or create project at ~/tmp/zedproject