Chakra is the new JScript engine developed by Microsoft for their upcoming Internet Explorer 9 (IE9) web browser. A distinctive feature of the engine is that it compiles scripts on a separate CPU core, parallel to the web browser. Chakra improves the performance of the browser and the web pages render and respond much faster.
You can read more details on Chakra at TechNet.
Try the Internet Explorer Platform Preview 4 and its demos, here.