Here are links to  nonprofit organizations we've found helpful over the years. Happy to add if you've got any to suggest; reciprocal links much appreciated.

AAAS
Biotechnology Industry Assn.
Boston Meetup
Boston SEO Meetup
Cambridge Community Television
Columbia Club of New England
Columbia Journalism Alumni
 Cornell Club of Boston
Healthcare Businesswomen's Assn.
Mass Bio
Jewish Vocational Service
Mass Life Sciences Center
Mass Technology Leadership Council
Medical Development Group
National Writers Union
Nieman Foundation for Journalism
PEN New England
Public Relations Society of America/Boston Chapter
Publicity Club of New England

The Write Stuff (Lincoln, MA library)
Women Entrepreneurs in Science and Technology (WEST)