GlassFrog allows each member of the organization to make a project they own visible only to members inside the circle where the role is held. 

To do this, simply check the box next to "Private to circle" for a new or existing project and then click Save

Note that this will also have the effect of making the project private to the circle even if the GlassFrog organization has been marked as public.  See more information on this premium feature here.