Salesforce has launched a new UI which is called lightning design system. This is very sharp and neat UI. But salesforce yet not providing any JS framework for SLDS(salesforce lightning design system).
I am facing a problem with JS for SLDS. Are you also facing problems? I found two of JS framework. They both are providing JS for SLDS.
Click Here to Getting Started with ALJS.
The Framework is not dependent on salesforce.com functionality or context and can be used independently.
Click Here to Getting Started with Lightning Dart.
If you know some other JS frameworks. Please type in comments. I will add here. Make it useful for others.