Nanobreweries are hot—these tiny breweries seem to be popping up all over the craft beer scene. While exact definitions regarding 'how small is small' may lead to debate over a pint for three, it seems to be generally-agreed-upon that nanobreweries are, as their name implies, really quite wee, and by both design and practicality, they are aimed at their immediate local market. Some are in operation as small-scale brewpubs, while others simply make beer and sell it directly to consumers or via local bars and restaurants. There are now more than sixty of these very small breweries in the US, and there could be more than 100 by the end of the year.
They are not to be confused with 'gypsy' brewers, who typically brew on the premises of other breweries (either solo or in collaboration with that brewery); rather, nanobrewery founders are investing in their own equipment, real estate and ingredients to get their businesses up and running. Some begin as one-person operations (often stepping up from homebrewing), while others start off with a number of partners.
A few nanobrewers simply like the flexibility offered by the small-batch approach; it means the available beers will be in constant rotation, with ample room to experiment with new styles (and less investment of time and materials is required if a particular batch isn't quite up to snuff), while others have a goal of starting small and growing into a microbrewery in the future. Other nanobrewers even look to give people a leg up into the brewing profession; New Hampshire's White Birch Brewing keeps their batch sizes small, but they offer an apprentice program to give would-be brewers and brewsters an opportunity to get involved in every aspect of brewing—including getting their beer sold to the public.
While nanobrewing seems like a recent trend, it sounds an awful lot like the way brewing operated until large-scale commercial brewers took over. Until the 19th century, small-scale brewing aimed at the local community was the norm. Coaching inns along old roadways in Europe and North America provided travelers with locally-sourced food and drink (though today's locavore might be rather disturbed by the wide variations in quality and freshness that prevailed at the time).
And in some ways, the current disagreements over how to define 'nanobrewery' versus 'microbrewery' (and any level of granularity beyond one might like to add) also mirror the past: in Britain, the Country Brewers' Society was founded in 1822 to act as a voice for smaller regional brewers as the larger breweries began to grow far beyond their original customer bases—although it should be noted that they were eventually folded into the much larger Brewers' Society.
The founding of the County Brewers' Society coincided with the growth of the tied house system, wherein large brewers took on pub ownership and dictated what their tenants would serve; the period from 1815-1860 saw most British pubs go from being owned and operated by someone who was very frequently brewing and serving their own beer to simply accepting deliveries from a corporate brewer—a similar trend was seen in much of continental Europe as well, although some individual cities continued to encourage small producers making their own beer (especially in parts of what are now Germany, Poland and the Czech Republic). A few of those brewers that survived and are thriving today would easily have been recognized as nanobreweries had they been transported to modern times—now, their products are available worldwide—consider a beer like Bamberg's Aecht Schlenkerla.
For those nanobreweries not looking to stay small, they are probably aiming for slightly faster growth, but being in business for centuries is not a poor model to follow.