Decimal time: Repeated several times in various countries, this hoax involves claiming that the time system will be changed to one in which units of time are based on powers of 10.
Write-only memory: Signetics advertised write-only memory (WOM) IC databooks in 1972 through the late 1970s.
Taco Liberty Bell: In 1996, Taco Bell took out a full-page advertisement in The New York Times announcing that they had purchased the Liberty Bell to "reduce the country's debt" and renamed it the "Taco Liberty Bell". When asked about the sale, White House press secretary Mike McCurry replied tongue-in-cheek that the Lincoln Memorial had also been sold and would henceforth be known as the Lincoln Mercury Memorial.
Left-handed Whoppers: In 1998, Burger King ran an ad in USA Today, saying that people could get a Whopper for left-handed people whose condiments were designed to drip out of the right side. Not only did customers order the new burgers, but some specifically requested the "old", right-handed burger.
Apple buys the Beatles: In 2010, Bob Lefsetz released an April Fools' Day letter which had rumours circulating around the music industry. In 1983, Australian millionaire businessman Dick Smith claimed to have towed an iceberg from Antarctica to Sydney Harbour. He used a barge covered with white plastic and fire extinguisher foam to convince witnesses. [wikipedia.org]