What company handles the exchange back end?
I had thought that Buttercoin was mostly a closed source system, in which the only thing the released as free open source software was basically a sale funnal site that sends all the actual work to their servers, so that all it let you do was put your own logos on your own site while really sending all the actual trading / offers to their servers?
-MarkM-
Buttercoin has not been updated for a while (couple months) on github so not sure if abandoned or working perfectly. To answer you question I think the entire thing is open-source you can even get the trading engine here :
https://github.com/buttercoin/buttercoin-engine