I used to think everyone knew how to play Ghost, but that turns out not to be the case. So here's an explanation of the game before I get into variants:
The game of Ghost involves spelling a word, with each player in turn adding a letter to a growing word. The object is to avoid being the player who says the last letter of the word.
To start, one player says a letter. The next player then thinks of (but doesn't reveal) a word which starts with the given letter, and says the first two letters of that word. The next player thinks of a word which starts with those two letters, and says the first three letters of that word. Play continues in this fashion until someone spells an entire word more than three letters long; the player who completes a word loses the round. If on your turn you don't believe the previous player was thinking of a real word, you can challenge that player; the loser of a challenge loses the round.
Here's a sample round with three players:
Adrian [thinking of "toast," though it hardly matters what he's thinking of for the first letter]: T
Beulah [thinking of "tadpole"]: TA
Charlemagne [thinking of "tatting"]: TAT [which is a word, but only three letters long, so Charley is safe.]
Adrian [now thinking of "tattoo," since "tadpole" no longer fits the current string of letters]: TATT
Beulah [also thinking of "tattoo"; since that has six letters, the final letter will fall to Charlemagne, so Beulah is safe in continuing the word]: TATTO
Charlemagne [can do one of three things: finish the word "tattoo" and lose this round; challenge Beulah in case she was bluffing (which seems unlikely); or bluff. In desperation, he tries the third tactic]: TATTON
Adrian [after thinking for a minute]: I challenge you. There's no word that starts out like that.
Charlemagne [shrugs]: Oh, well, it was worth a try.
Note that you have to be careful not to complete a word which is part of some other word. If the current string of letters is "DIFFE," and you're thinking of "difference" so you add an R, you've spelled the word DIFFER and you lose the round even though you didn't spell the word you were thinking of.
If you lose a round, you're assigned a letter: first G, then H, then O, and so on; when you've lost five rounds (spelling GHOST), you're out of the game.
Of course, the usual word-game rules apply: no proper nouns allowed, some agreed-upon dictionary as final arbiter of disagreements, and so on.
Now, those of you who learned to play Ghost as kids may be tired of the game. It's fun, but it's not often much of a challenge. And there often gets to be a certain inevitability to a round of Ghost, when everyone is heading toward the same word and some poor schlump is forced into finishing it.
So a while back, a friend introduced me to a variant: Superghost. In Superghost, you can add a letter either at the end of the growing word or at the beginning. Like this:
Dora [thinking of "ebullient"]: B
Elmer [thinking of "budge"]: BU
Frances [thinking of "ambulance"]: BUL
Dora [still wants to try for "ebullient," but can't add an L or she'll spell "bull" and lose the round]: EBUL
Elmer: Hey! ...oh, that's right, this is Superghost. Um. EBULL
Frances: Aha. EBULLI
Dora: May as well give up now, Frances. EBULLIE
Frances: Not so fast. EBULLIENC
Dora: Argh. Hoist by my own petard. Okay, 'E.' You got me.
Of course, this is Superghost, so in theory you get to lose ten rounds (one for each letter in the game's name) before you're out of the game. In practice, games don't usually last that long.
And finally, the ultimate in apparition-based spelling games: Superduperghost. In this variant, you can add a letter anywhere in the growing word: beginning, end, or middle. This game tends to result in very long silences as people try to figure out words to use.
Ignatz: EEEEER (that was five Es, right?)
Ignatz: BEEKEEPER. [sigh.] I just couldn't resist the chance to say five Es.
Superduperghost is a lot of fun when played with the right people, but it's rare that anybody's up for more than a couple of rounds of it, especially given the occasional several-minute wait between letters. Perhaps a good candidate for email play? No fair using a computer program to find words.
To extend Ghost in another direction, try playing sentence ghost, also known as "Cheddar Gorge," apparently played regularly on the BBC show I'm Sorry, I Haven't a Clue.