[pjd]

I would guess that what they're talking about is a so-called Oxyhydrogen (or Brown's gas) generator. This technology has been around for a long time and is not uncommon in certain welding applications. You can read about the process here: http://www.hhogasgenerator.com/.

An excerpt:
Oxyhydrogen is a mixture of hydrogen and oxygen gases, typically in a 2:1 atomic ratio; the same proportion as water. At normal temperature and pressure, oxyhydrogen can burn when it is between about 4% and 94% hydrogen by volume, with a flame temperature around 2000 C.

Oxyhydrogen will combust (turning into water vapor and releasing energy which sustains the reaction) when brought to its autoignition temperature. For a stoichiometric mixture at normal atmospheric pressure, this is about 570 C (1065 F). The minimum energy required to ignite such a mixture with a spark is about 0.02 millijoules.

[far sider]

"runs on nothing but water..."

Yeah. And I have a fireplace that burns on nothing but ashes, and lately I've started breathing nothing but carbon dioxide.

[E. Pluribus Unum]

Thank God they repealed the First Law of Thermodynamics, otherwise this wouldn't work because it takes the same amount of energy to break the hydrogen-oxygen bond as you get when you create it by combustion.

[E. Pluribus Unum]

Proof the HHO is a scam.

[Mr. Dough]

Great, now along with Global Warming we're going to have to worry about Global Drying, because these guys are breaking apart all the water molecules!

[count-your-change]

It appears the engine spins on hot air supported by euphoria and fueled by transparent hype.

[Kevmo]

For the renewable energy ping list. This appears to be a cheap way to use electrolysis to split up H2O and then run a hydrogen engine from the 2H.