HTC HD2 has got lots of unofficial development. Born with Windows Mobile 6.5, developers got it running Android (up to KitKat!), Windows Phone 7 and some Linux distributions.
Most of the credit goes to the Dark Forces Team, some great developers that made the HD2 run also Windows Phone 8 and Windows 8 RT; even if they didn’t release anything.
Following one of the members on Twitter, however, I found that they were also working on another great operating system: iOS 4!