Is there an open source program that would give you the "Pages" feature of Backpack (37Signals)?

Question

I'm creating a financial web app (Rails 3) and I would love to put a feature in such as the one from Backpack's "Pages" feature (from 37Signals).

I could probably just use some JS WYSIWYG plugin but I really like that feature of Backpack.

Thanks for any recommendations.