Brettanomyces (brett.) is a wild yeast commonly used in the secondary fermentation of many Belgian ales. The yeast produces both earthy (barnyard, horse blanket) and fruity ester (cherry pie, pineapple) flavor and aromas. The most well-known Belgian beer with brett is Orval. Belgian Lambics also contain brett, but often the dominant flavor in these beers is the souring bacteria of lactobacillus and acetobacter. US breweries doing the brett-thing are Jolly Pumpkin in the Ann Arbor area, Dog Fish Head and Russian River out of Sonoma County, CA. Best to give it a go yourself.