MyBitcoin used to be an online Bitcoin shared eWallet. It was the go-to place for easily handling bitcoins. The site eventually shut down with a major loss of coins, widely suspected to be perpetrated by the service operator.
Its time of closing down is well known (July 2011) but I could not find a reference for when it was opened.
(Potentially relevant reading: What is the story behind MyBitcoin?, How much Bitcoin was lost in the Jul. 2011 MyBitcoin site shutdown incident?)