Greentown Labs, now home to 20+ start-ups, is the second largest cleantech incubator in the country, with a very unique offering - 19,000 square feet of prototyping space as well as office space, in an urban location, Boston's Innovation District. Since opening its doors in May 2011, Greentown Labs has served 25 clean energy and clean technology start-up companies; its member companies have raised over $20M in capital and employ nearly 80 people.