As for PayMeNow, yes, we wrote an interface for this in our medical software, but this is not part of the SF framework (yet anyway). If you are trying to interface with PayMeNow I would be happy to share some of that logic if that is where you are trying to go.
If I recall, PayMeNow was one of the easiest to interface with as they had very clear and concise instructions for the http web request and response. It took around 30-60 minutes to create an interface for them. Posting our code will not be as much of an option as we have abstracted our interface so that we can communicate with other online processing companies as well.