The digital entrepreneurs first worked together years ago on Mapping Main Street, an interactive project created in collaboration with journalist Ann Heppermann and supported by Harvard’s Berkman Center for Internet & Society and the Association of Independents in Radio. Jammed into a 1996 Subaru station wagon, they set off along a 15,000-mile journey to make audio and video documentaries of American streets named “Main.” Today, the site invites collaborators nationwide to furnish more stories of America’s Main Streets — an estimated 10,466 of them.