There's also a decentralised imageboard called NNTP-Overchan
http://topchan.xyz/static/faq.html
A few frontends:
http://oniichanylo2tsi4.onion/
http://topchan.xyz/ or http://topchanjgbabhkmb.onion/
http://i2p.rocks/
http://lp4t52xp5vlhyhkb.onion/
http://slamspeechicukxu.onion/ -No images - down atm