I'm familiar with the Google Traceur project (which is considered ready for production use in critical systems) as a transpiler from ECMAScript 6 to ECMAScript 5; unfortunately I still have to support IE 8 which is only compatible up to ECMAScript 3!
I'm curious if there are any projects out there to transpile from ECMAScript 6 to ECMAScript 3 so that I would be able to start utilizing ECMAScript 6 functionality now and then just switch over to that code base once IE8 is finally deprecated.