The "collaboration beer" has come a long way over the last decade. One early example that put the concept on the map was "Collaboration not Litigation," a brew created in tandem by Russian River Brewing and Avery Brewing when they discovered that they both made a beer called "Salvation." Rather than sue the pants off of each other, they created a unique blend that showcased both of the brewery's strengths. Since then, many breweries have built collaboration beers into the core of their identity. Stone Brewing, for example, releases beers made in conjunction with other breweries every couple months.
Prairie Artisan Ales