Zenburn is a low-contrast theme meant for long coding sessions. It was originally a vim theme, but it's grown from there.
This theme for Atom is based on Colin T.A. Gray's version for TextMate.
Like it, it's released under the terms of the MIT license.
I've not tested it with anything except Ruby and Markdown, and both seem to work fine. Because it's a conversion theme, everything that was supported in TextMate should be supported in Atom.
To release a new version, ensure that everything is set on master and do apm publish.
If you forget and manually tag, use apm publish -t <tag>.