Natto is a fermented soybean produce from Japan, where its health benefits are widely known. It is high in calcium, vitamins B and K, and soy isoflavines, and is proven to inhibit blood clotting, reducing the risk of strokes or heart attacks. Some claim it fights cancer, aids digestion, aids weight loss and lowers cholesterol, but scientific data for these claims is debatable. Natto has a funky smell, but tastes nutty and mildly pungent. If you liked pungent cheeses like bleu cheese or brie before becoming vegan, then you might like natto. Natto also has a weird sticky, stringy, slippery texture--this, plus the smell, turn a lot of people off. But if you can develop a taste for it, you'll find it addictive. It is available in the US at some Asian groceries. Usually natto is sold in sets of 3 or 4 50-gram packages. I would recommend asking your local health food store to order some. Because of its benefits, it ought to be more widely distributed as a health food.
Here is one of the basic ways to consume natto in Japan: Open one package of natto and mix in soy sauce and spicy mustard to taste. Some natto packages come with a little packet of mustard and tare sauce, which contains soy sauce and mirin (sweet sake). Finely chop a teaspoon of green onions or chives and mix into the natto. Note that natto will get more viscous and stringy the more you stir it. Put natto on top of a bowl of steaming hot rice. Enjoy!