Yes, i was talking about the letterzines via snail mail.
They died out after a significant portion of fandom got computers. I bought my first one in 1995. Around then a lot of fanfic was already appearing online first on newsgroups. I think the ones i have are from
the late 80's early 90's. Some of them came out relatively often, monthly or bi monthly. I guess they could maybe be considered fannish social networking to an extent. It was a long time in between comventions when you could talk with other fans.
