7Chan is one of those boards that has been around for quite some time. I actually remember back in my days of being a weird teenager that I'd navigate between here, 4chan and Ebaum's World (shudder). Anyway, if you're not familiar with what a chan is, basically it's a way for people to share porn images anonymously and in a board-type fashion. It's sort of like a forum, but posts don't last too long and there's a lot of 'original content'. People love OC, because it's amateur and raw.
The niches covered by 7Chan are varied, with lots of the classic hentai-style porn as well as special interest stuff such as traps (transsexuals), furries, uniforms and even a place for you to share and read some erotic literature.
Be warned, *chans have a special ability to attract some really weird people that do some really weird shit. It isn't for the weak willed and expect to be offended or made a little queasy once or twice. The Internet is a strange place, and 7Chan will show you why.