The Double Data-Interface-Presenter Pattern
In this pattern, the Presenter of the first application becomes the Data of the second application, kind of like a Dual-MVC, but using presenter logic rather than a dumb template / view.
I'm building a toolkit to make a variety of web applications with incredible user interfaces at incredible speed... so far it's been a long slow process of finding the right tools for my toolkit, but things are shaping up.
Apache (good enough for now)
Ruby on Rails (My favorite web service framework)
JSON (a subset of YAML / YML)
and a sprinkling of Google's magic here and there.
and a heavy dose of figuring out how to perform local caches
and a spattering of forwards-compatible HTML5 semantic classes