Ask HN: Most Innovative Web Frameworks in 2012?

Almost all of my software development over the past 3 years has been spent building web applications. I build mainly small to medium scale sites (read couple hundred to several thousand daily hits), ecommerce shops, the whole gambit and along the way I've used and tried out tons of Framworks, CMS solutions, etc. I like Rails, Play and Symfony2, and have recently discovered Lift (still haven't made a project with it) but it looks promising. The thing is you can basically build anything regardless, but because I build largely interactive apps ( ajax, server pushing, parallel page rendering, etc), I'm always on the lookout for a good fit in this sector. Anyway, I'd be really interested to know what toolsets (front and backend), my fellow hackers use now in 2012 to build RIA :)