Hundreds of years ago, whoever controlled the ports of the world controlled the empire. In the Android world, ports rule once again -- in particular, a developer named Hashcode's port of Android 4.1 Jelly Bean to the Amazon Kindle Fire totally rules.
The initial build isn't perfect -- there are issues with enabling Wi-Fi and some video codec -- but besides a few little bugs, it more or less transforms the user interface on the Fire into what you'd see on a Google Nexus 7. Keep in mind that these sorts of operations always come with some level of risk, including the possibility that your Fire could be transformed into a brick-like piece of burnt toast.
Take a gander at what it looks like to toss a Jelly Bean into the Fire in the video below: