There are quite a few:
1) ghost: each player says a letter. If you form a word with more than three letters, you lose a point, thus earning one letter towards being a "ghost". Usually the word that is being constructed is a known word, like "platter", or "season". However, you are entitled to "bluffing", so if the first two people say "p" and "l", you can say "x", for instance. Now, if you do this, the next person can call the bluff by saying "I callenge you". Then, if you can think of a word that begins with "plx" (in this case you won't), then you lose a point. If, on the other hand, you come up with a word that begins with those letters, the "challenger" loses a point. The tricky thing about it is you might be the fourth person, the other three said m, o, and t, so you think "mother", and say h. This means you formed a word, because you spelled "moth". If the next one doesn't notice, you're safe.
Names of people or places don't count.
An example: Five players (there can be large numbers, but at least three): Player number one says G, number two says R, three says A, four says P - now, number five might think he is in a tight spot, because it seems the only possible word is "grape". But number five may say P, forcing the word "grapple", which will end on player number two. Then you say the player who lost a point is a "G" (starting to become a ghost), and that player begins the next round. Let's say she or he says "S", then the next says "U", then the next "R", the next another "R", the next player says "E", and now it is the turn of the one who began this round with "S" - but s/he cannot think of a word that begins with "surre...", and challenges the one before, who said "E". The one who said "E" will say that the word being formed is "surrender", and then the challenger, who was a "G", becomes a "GH" - one more step towards being a "GHOST". Those who become ghosts leave game and the rest continue, until only one player is left - the winner!!!