[tlack]

This looks like another great alternative to JsFiddle/Plunkr (both of which are excellent).

One question though: why is my download button grayed out?

[remysharp]

Download will only be downloaded in the initial state of jsbin - i.e. if there's nothing to download. When you type, it'll save your bin and you can download that. You can also directly access each panel on the url, like jsbin.com/abc.css or jsbin.com/abc.less, etc.