Pool is part of a wide variety of cue sports, and includes billiards, snooker, and carom. Hey, I used to have a carrom game when I was a kid, although I probably didn't play it according to the rules.
|The cheap, Americanized version with the plastic rings that also lets you play chess, checkers, and backgammon on it.|
One variant I've played since I was a kid, especially when playing by myself, is simply that you have to knock all the balls in in numerical order. You have to drop ball 1 before you can go for ball 2, and so forth, until you drop ball 15 in last. In this game the 8 ball is nothing special, just another ball to knock in after the 7 and before the 9. I mistakenly called it Nine Ball, but apparently, that's a rather different game than what I played.
|Pictured: A Nine-Ball rack|
Much more recently, I came up with a simple variant on Eight-Ball that I rather like, based on the colors of the balls. At first, you can knock in any ball you want to, except for the 8-ball, but when you knock in one ball, you have to go after the other ball of the same color before you're free to shoot at any other balls. So, for example, if you knock in the 10 ball, which is blue, you have to go after the blue 2 ball before you're free to shoot any other balls.
Furthermore, if, while going for the 2 ball, you accidentally knock in the green 6 ball, you now have to shoot for the blue 2 and the green 14 ball before you're free to shoot at any other balls. Any other player can shoot your balls in for you with no penalty, but then, why would they want to help you? ;-) Once all the other balls are in, then the players can shoot for the 8-ball.
This variant has several interesting features. For one thing, it's just as easy for 3 players to play as it is for 2 or 4 players, as there's no need for teams. It also creates a tremendous but temporary challenge as you are restricted to getting both balls of the same color before being free to shoot at any other ball. This variant also makes a good handicap game for widely mismatched players, as a good player could knock in most of the colored pairs, but still lose if the weak player ends up knocking in the 8-ball at the end. Unless you want to keep track of how many colored pairs each player knocks in. Then, of course, the stronger player has the advantage.
Obviously, these rules aren't set in stone, so feel free to modify them as you see fit. But I think it's a nice variation, especially if you're just playing for fun.
Upon checking, I found one variant that is somewhat similar to mine, although not exactly the same: Cribbage Pool. In Cribbage, instead of knocking in pairs of the same color, you have to knock in pairs that add up to 15. For example, if you knock in the 6 ball, you next have to knock in the 9 ball. There are some other differences, as well, but it is at least similar to my variant.
I gave it a try, and I'd say Cribbage is much more difficult than my variant. With my variant, if you don't drop the matching colored ball, then you just keep trying (when it's your turn again) until you do. With Cribbage, if you don't make the matching ball, then the first ball that you dropped gets put back on the table. If you're not very good at pool, a Cribbage game can last a long time.
So go play some pool! And let me know if you like my variation on Eight-Ball in the comments. Oh, and Merry Christmas and Happy Holidays and all that stuff...