The Good Parts (tm) Super old and works everywhere. Easy to implement. Server-side or Client-side rendered. Encapsulated. UI platform agnostic. Communication via postMessage.
paypal.com/myaccount/transfer?redirectUrl=/merchant/home 1. Store redirectUrl in session. 2. /myaccount/transfer is rendered. 3. If the user exits, redirect to redirectUrl. 4. If the user completes, redirect to redirectUrl.
Next steps Split out as many apps as possible. Keep building server-side modules. Build UI components for dust/Backbone. Hopefully within 2-3 months =)