Robin Good: Thimble is a new web editor from Mozilla that makes it very easy for anyone to create and share their own web pages.
From the official site: "It’s an intuitive visual editor that lets you write and edit HTML right in your browser, preview and correct your work, and then publish and share fully functional web pages with a single click.
Thimble removes many of the barriers for novice users trying to learn code, and includes a series of starter projects and templates to help anyone get started quickly."
"Write and edit HTML and CSS right in your browser. Instantly preview your work. Then host and share your finished projects with a single click."
Find out more: https://thimble.webmaker.org/en-US/
Check also: http://blog.mozilla.org/blog/2012/06/18/introducing_thimble/
and: http://webmaker.org/