The lightning design system is a very sharp and neat UI. But Salesforce yet not providing any JS framework for SLDS(salesforce lightning design system).
I found two of the JS frameworks. They both are providing JS for SLDS.
A. Appiphony Lightning JS (ALJS):
Get Started with ALJS.
B. Lightning Dart:
The Framework is not dependent on salesforce.com functionality or context and can be used independently. Get Started with Lightning Dart.
If you know some other JS frameworks. Please type in the comments. I will add it here. Make it useful for others.
Thanks. Happy SLDS!!!