The HTC HD2 had the misfortune of not getting updated to Windows Phone 7 even though it had more than capable hardware at the time. However, thanks to the efforts of the hacker community, the device is still alive and kicking with latest versions of numerous operating systems such as Android Marshmallow, which was recently ported to the device.
It has been just under a year since Lollipop was ported to the mighty HD2 with most features working and now the folks at XDA-Developers have managed to do the same with Android's latest version. Ironically, Marshmallow is yet to reach many of the currently supported smartphones.
According to XDA-Developers member macs18max, the HD2 Marshmallow port based on CyanogenMod 13 isn't feature complete and only the display, Wi-Fi and audio are usable. There's no word on whether it will be be able to access a cellular network anytime soon, so the build isn't very useful for now.
Some of the other operating systems that were ported to the HD2 in the past include Windows Phone 7, Windows Phone 8, Windows RT and Firefox OS, as well as Android versions 2.2 Froyo, 2.3 Gingerbread, 4.0.4 Ice Cream Sandwich, 4.1 to 4.3 Jelly Bean and 4.4 KitKat.
If you have a HD2 lying around somewhere and want to kill time during the weekend, you can grab the experimental build and flash it to the device, of course at your own risk.