The professional networking site LinkedIn.com has "groups" which people can join to discuss topics of particular interest. Anyone can start a group, and they are termed the "owner" of the group. The "owner" determines who may join the group, moderates the discussions, can delete comments, discussions etc.
On LinkedIn, many of these groups are for members of dues-paying trade organizations, birds-of-a-feather interest groups, and "Alumni of..." various companies or educational institutions.