HTC's chameleon-like HD2 just refuses to die. The phone was introduced back in late 2009 (around the same time as the original Motorola Droid and Android 2.0, for reference) and ran the now-dead Windows Mobile platform, but enterprising users have hacked a wide variety of different, more modern operating systems onto the device. We've already seen semi-functional versions of Windows Phone 7.5 and Android 4.0 running on the device, so its not a shocker to learn that Android 4.1 (better known as Jelly Bean) has now been ported over by the xda-developers community.
Also unsurprising is the fact that the release is described as a "pre-alpha" — there's a number of features not working exactly right, including Google Now, the browser, the camera, and some app installs. Of course, there's a lot that does appear to be functioning, including mobile data, phone calls, Bluetooth, Wi-Fi, and SMS. While you might not want to rely on this phone and this custom ROM as your daily driver, you should be able to get a taste of Google's latest OS if you give this hack a shot.