I'm sorry to be late to the discussion, but I was excited to see that Mozilla Webmaker's Thimble was included in the list of free editors. I've used it in instruction and it's a great tool. But I wanted to add a quick note about Thimble- the entire Webmaker site is being revamped along with Thimble (https://blog.webmaker.org/whats-next-for-webmaker-tools). It will be updated and will be moved to the teach.mozilla.org site later this year (https://blog.webmaker.org/whats-next-for-thimble). So keep an eye out for these updates and know that the URL will change.
I'd also recommend three other web-based editors (or "code playgrounds"): JSBin (http://jsbin.com/), JSFiddle (http://jsfiddle.net/), and Bootply (http://www.bootply.com/). These three are all very similar to Thimble except that they have separate input fields for HTML, CSS and JS. They also allow you to quickly link various frameworks and libraries by simply selecting options from dropdown menus. I have used JSBin in teaching web development and have found to it be very useful for setting up exercises, remixable templates and examples. I have even created informational webpages for workshops on the fly. JSBin also features very simple URLs that are 'pronounceable' and easy to remember and share. Since JSBin is open source, it can also be downloaded (https://github.com/jsbin/jsbin) and installed locally, though I've never done this so I can't speak to the difficulty or ease of setting it up. JSFiddle has very similar functionality- I prefer JSBin's UI and the fact that it's open source, but they're really very similar. Bootply is basically the same as JSFiddle but allows you to plug in Bootstrap elements and build Bootstrap templates quickly and easily. This program makes it very easy to teach and demo Bootstrap. All of these programs are all free to use, with or without accounts.
Timothy W. Miller
General Instruction & Reference Librarian
Kinesiology, Recreation Administration, and Environmental Science
Humboldt State University Library
One Harpst Street, Arcata, CA 95521
Office: Library 2
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