Most skeptics are aware that the Ouija Board as used in seances, demon summoning and all the best horror films was a child's toy, invented in 1890. The details are that Elijah Bond patented a board marked with 0-9 and A-Z, along with Yes/No and Hello/Goodbye combined with a heart-shaped planchette as a parlour game. It was the addition of the planchette that was different, 'talking boards' had already existed, with spiritualists using a pointer of some sort to spell out messages from the dead. Bond simply standardised and codified the idea of a simple marked board and planchette together and marketed it as a game. One of his employees, William Fund, took over management of the game's production and remarketed it as the Ouija board (there are various explanations of the name, some say it is French Oui with German Ja, others that it an ancient Egyptian word for good luck and Fuld himself claimed that he "asked the board"; Ouija is what it spelled out). Fuld marketed the board as: "Surpasses, in its unique results, mind reading, clairvoyance and second sight. It furnishes never failing amusement and recreation for the entire family...Ouija gives you entertainment you have never experienced...Unquestionably the most fascinating entertainment for modern people and modern life".
It was a huge success and spawned numerous copies which resulted in lots of acrimonious lawsuits over patents. By the 1920's talking boards were hugely popular. However, almost from its invention, Ouija boards have been the subject of dire warnings from religious organisations. Many have accused players of meddling in satanic forces and some publications claimed that adherents had summoned the Devil through their use. Its use in the 1973 film The Exorcist (12-year-old Regan plays with a Ouija board and meets a new imaginary friend she names Captain Howdy, turns out Captain Howdy is actually “the devil himself") reinvigorated its popularity and it has become a staple of horror movies. The game still sells well and the patent is owned by Hasbro in the USA.
But what allows the planchette to seemingly point to letters on their own? If you've ever played with one, you will realise that it is quite disconcerting to find the pointer moving seemingly with no direction from your fingers. Of course, you have no way of knowing if your co-players are the ones moving it but there is of course the ideomotor effect, where slight, almost unconscious movements are made, especially when muscles are under stress of trying not to move them. Though could it really be the Devil? He would want you to think it wasn't, wouldn't he...?