Another similar project is django-bursar[1] which is supposed to be integrated into the Satchmo[2] webshop in the (far) future.
At this point, we've created our own payment gateway wrapper. At an API level, it doesn't look terribly different from Paython, so I'm cautiously hopeful that we'll be able to port our PayFlow Pro and stored credit gateway backends if it looks like Paython is gaining traction.