Futaba Channel
Futaba Channel (or confusingly, 2chan) is Japan's most popular Imageboard. Users with IP addresses that can't be traced back to Japan cannot post.
Origin
Futaba was designed to be the 4th main site of Nanashi World in case the current one, 2ch, broke down. The community has since diverged greatly from it's predecessor.
Futaba Channel was extremely popular on Something Awful's ADTRW boards, as it's anonymous image posting system was important in an era before image hosting. The site inspired moot to create 4chan, and it's code, Futalullaby, formed the basis of 4chan's Yotsuba codebase (though by now it has been heavily rewritten).
Raids
Futaba is home to epic raids that you can't participate in.
External links
Futaba Channel Futaba Navigation Society JKid - Futaba Channel (The Third Channel)