Billionaire Microsoft co-founder Paul Allen no longer owns one of the world's 10 largest yachts thanks to the just-launched Serene (above) from Fincantieri. At just under 440 ft. Serene is the largest yacht ever built in Italy, and enters the list of the world's largest yachts at No. 9, according to Camper & Nicholsons – just behind the floating brothel Savarona. That knocks Allen's famed 414-ft. Octopus out of the top 10 altogether (No. 1 of course is still, by a mere 18 inches, Roman Abramovich's Eclipse). The billionaire buyer of Serene is unknown. Designed by Espen Oeino, the Serene, which took four years to complete, has seven decks, a tender hangar and two helipads. The high-tech megayacht features a large seawater swimming pool and a submarine with a diving depth of up to 100 metres. The 4,500 square meter interior boasts super-luxe accommodations and entertaining spaces designed by Pascale Reymond of London's Reymond Langton Design.