Over the years, we have seen the HTC HD2 run the forked version of Android employed by the Nokia X, FirefoxOS, Windows RT (!), Windows Phone 8, Windows Phone 7.5, and dual boot Android and Windows Phone 7. Speaking of Android, the HTC HD2 has been fitted with KitKat, JellyBean and Froyo.
The Android 5.0.1 ROM is said to be in early alpha build, and only the display and audio are working at this point. But XDA member macs18max says that he will continue to work on the port.
There you have it. The majority of Android devices have yet to be updated with Android 5.0, but a Windows Mobile powered phone from 2009 is running Lollipop (albeit with limited capabilities).