4chan Boards

Boards sharing a letter
Several boards have used the same letter as another board at a different point in time. Usually, this occurs when a single-letter board is deleted and its letter is later re-used.


 * /g/ - Guro, Technology
 * /n/ - Trains, Nature & Wildlife, News, Transportation
 * /p/ - Photo, Photography
 * /x/ - General Photo, Paranormal

Secret boards
There were two secret boards I knew of. The first was /5/, which was for posting pictures of 5. The second was /z/, an exile board detailed at Everything Shii Knows.

Further information
Everything Shii Knows has an article on 4chan.