Kingdom of Loathing
Kingdom of Loathing is an MMORPG (sort of) that features a level dedicated to NetHack. This area has several monsters and items from NetHack (including the Amulet of Yendor) and contains several references to NetHack.
The devnull tournament achieved the reverse in 2005, patching NetHack to add an area dedicated to the Kingdom of Loathing. The trophy description states that "players accepting this Challenge must venture to the Kingdom of Loathing to defeat an alternate-universe Wizard of Yendor".