WWDC 2018 takes place June 4 to June 8 in San Jose, California.
Tiger Release Date?
Amazon has frequently posted unofficial release dates on pre-release items, and this likely does not represent any inside knowledge.
Apple first announced Tiger at WWDC 2004 and stated that it would be released in the first half of 2005.
Update: Amazon.com has removed the March 31st release date. The product page now reads, "This item is not stocked or has been discontinued."