I was wondering if it might be Yahoo Groups. There's so much old fannish content there, and frankly it surprises me that the site still exists. I can't imagine it's much of a moneymaker even if there are pockets of activity.

Now that Verizon's got it, I have to wonder how many days it has left. It's probably not costing them money like Tumblr did but I expect its sale probably means the sale or shutdown of a number of other Yahoo properties.
When it goes down it's going to be like Geocities all over again.