Dave Winer uses analogy to distinguish Frontier, the environment (framework?) Manilla runs on, from Radio. He writes:

Frontier is our mainframe. It’s centralized. It includes Manila, a deep and powerful browser-based content management system. Where Radio is designed for individuals, Frontier is designed for communities and organizations, workgroups—groups of people.

I think that’s key. But it also seems to me that an organization running Frontier/Manilla might still want to license Radio for its end users.

I’m still struggling to grasp Radio. It’s so enormously powerful, with so much potential that I find it slippery.