DAN KURZIUS

Chestnut and Kurzius are the founders of Mailchimp, an email marketing firm that’s a favorite among small-business owners. Before starting the business, Chestnut taught himself to build websites by reading technical books at Barnes & Noble, and Kurzius served as a part-time DJ and competitive skateboarder. Mailchimp began as a side project and took six years to become a full-blown company; it now generates more than $600 million in revenue.