>>192
It's an English knockoff of the most popular Japanese bulletin board, 2channel, except 2ch has millions of daily users and 4-ch has about four of them these days.

There is no particular focus for the site as a whole, but the most active board is "DQN," which is named after a 2ch slang term for dumbasses and has the kind of content you would expect given that.

4-ch used to have competing English websites, like world2ch and world4ch. Somehow it outlasted most of them.