Bob, The Floating Widget

The Floating Widget
Invented by Guinness in 1989, the widget sits at the bottom of the can of beer (be it stout or bitter) containing pressurised gas, which the bubbles through the liquid when the can is opened, imitating the foamy head created when pouring draught beer.
The fixed design was replaced with the floating widget in 1997, which is a hollow sphere 3 cm in diameter. The can is pressurized by adding liquid nitrogen, which evaporates after the can is sealed, forcing gas and beer into the widget's hollow interior through tiny holes. When the can is opened, the pressure in the can drops, causing the pressurized gas inside the widget to jet out from the holes. The holes in the widget are angled slightly so that the widget spins, creating a creamy head inside the can.
However the floating widget was only used in cans, for bottles another design was needed. And in 1999, Guiness came up with the Rocket Widget, another evolution of the idea. So whether you buy Guinness in a can, a bottle, or as a pint in a pub, it will always have it's creamy head.

Since it's conception many other beer companies have followed suit, I'm not sure whether they came up with their own systems or just licensed Guinness', but if you cut open any can of Murphy's, Caffery's, Boddington's or John Smith's Extra Smooth, you'll find a widget inside of the floating variety, with the exception of Caffery's, who use a fixed design.

Bob Smith
You may have seen the TV advertisements for John Smith's Extra Smooth beer, featuring there "no nonsense" theme and "Bob, The Floating Widget". Seeing as they called the widget in the can Bob, and the beer is made by John Smith, it seems reasonable that the full name of the widget would be "Bob Smith". So there you have it. Bob Smith is also the name I go by on the net (c'mon, almost nobody uses their real name), since I'm quite partial to a pint (or rather a 440ml can) or the stuff.