This was actually built between 2012-2013 - it is quite a tangle of old and rusty (but very reliable) PHP code and IE9-era, 'jQuery-esque' JavaScript. Realistically this can't be usefully made open source (and if it were it would probably have to be rewritten in order to be more generally useful). That said I would be very interested in an open source re-implementation of this using modern techniques!