There's at least one open source project[1] out there, something I think Red Hat may actually be involved with (or behind) for managing subscriptions and what-not. We haven't deployed it yet, as we aren't yet at the point of having paying customers. And if we signed a deal tomorrow we'd just keep track of things manually in the interim.

As for distribution... we're working on our own homegrown "customer portal" which will deal with downloads and what-not, as well as other "customer stuff".

[1]: http://www.candlepinproject.org/