It's "open-source" but the source isn't available and there's no way to contribute? Their website (armstrongcms.org) mentions they have a GitHub page, but it's not linked, and I'm not finding anything from searching repositories for "Armstrong."

EDIT: Ah, I see my GitHub search-fu is not strong, but jashkenas' is ( http://news.ycombinator.com/item?id=2313737 ).