It's a bit strange that Alexis Ohanian is listed as an "investor" in the page and also as a "founder" in the footer. I guess the footer isn't intended to mean that he's a founder of Buttercoin, but it sure is easy to misread it that way.
Unfortunately things didn't work out and the original open source effort died off when we decided to start with a fresh implementation. We just recently release the engine we're using (with some minor tweaks) under an MIT license here: https://github.com/buttercoin/engine. We'll be backporting a bit more functionality until we can actually run it in production.