Sync is an alternative to Ember/Backbone, but not a replacement. If you're trying to replicate desktop software in the browser for instance, a heavy client-side

Sync is an alternative to Ember/Backbone, but not a replacement. If you're trying to replicate desktop software in the browser for instance, a heavy client-side framework is the way to go; however, for certain use cases for web applications with lots of "richness" but not trying to replicate desktop level interactivity, think Basecamp, Reddit, Facebook, Twitter, the Sync approach could definitely hold its own against these types of apps. I've greatly enjoyed building Backbone apps, and I look forward to playing with Ember, but not every web application needs to be rendered client-side against a JSON api. Sync also allows you to wire up your own javascript, so you could even use backbone models submitting over JSON and render your realtime views with Sync on the server. I'm excited to see how far we can take this approach.