Its arginine alpha-ketogluterate,AKG,trade name is NO2. It was developed by the guy who launched creatine. The commercial site is getno2.com if you want to check it out.
Heres an excerpt:
Because Ed Byrd introduced both creatine and NO2, he says it best...
"As you probably know, creatine causes 'cell-volumizing' by pulling water into the small space 'inside' the muscle cell. It does increase size, but you may look a little 'puffy.' NO2's hemodilation, on the other hand, creates genuine size by forcing blood into the vast and voluminous spaces 'between' the muscle cells. Not 'inside' the cells. This 'super-engorging' creates massive pumps. What's more, because the blood is between the cells not inside them, the pump is rock-hard. Not 'puffy.'
And with the extended-release delivery system pHyser3, the pump does not go away. You get what's known as a 'perpetual pump.'
Frankly, my recommendation to bodybuilders would be to take both creatine and NO2. I look at it this way, what I started with creatine, I perfected with NO2."
How much of this is science and how much is marketing bullshit is the next question. I did find a few studies showing benificial effects of AKG. The cheapest price I've seen on it so far is at affordablesupplements.com (57$/month supply)