I just posted the general-billing and verisign APMs for MACS on the Ybos developer site. If you wanna convert them for OpenACS, you'll need to translate "del" functions to "delete".

Once Janine and Bart come out with their service-contract based gateways I'll probably adapt the general-billing package to work with those.

BTW, general-billing is designed so that it could be used as a skeleton that e-commerce could be laid over, and we will probably do that eventually, but if anyone wants to take a crack at it earlier, by all means do so.