Capture the Flag

Capture the Flag is a multiplayer game mode that Notch mentioned would be added to Minecraft in the future. Due to the time since an official implementation was mentioned, and that the game mode can be implemented with the use of command blocks and scoreboards, it is unlikely that it will be implemented as its own game mode.

The objective of the game mode is for two or more teams to try and capture a predetermined item, (most commonly a flag as the name would suggest), from the enemy base to their own and at the same time try to prevent any other teams from doing the same by killing them. The idea of implementing this game mode has received positive reactions from the community. Bows and other weapons such as swords will be dropped upon death and will not be taken from others.

Rules
Capture the flag is a game where there are two flags (or more), one for each team, and each side tries to capture/take the other team's flag and return it to their own side's base. You win when your team captures the other team's flag, however you will lose if they take your flag. Most games have a certain amount of times the flag should be captured. There is also one version of CTF in which you must take the neutral flag from the middle of the map and return it to the enemy base.

Unofficial implementation
Although the game mode itself has yet to be officially implemented into Minecraft, Capture the Flag is still played on some multiplayer servers, except instead of using a flag, a suitable drop item such as dirt, sand, wood or colored wool is used as a substitute. This is very much possible in "CraftBukkit" with multiple plugins. Another choice is to use TNT, since it can be placed on a redstone torch when attempting to return the flag to your base. Some servers also choose to have chests storing the "flags".

Some multiplayer servers, Classic and regular, choose to use modifications to further enhance the experience of Capture the Flag. Coded signs, block formations, or added blocks can also be used to play Capture The Flag.

Using command blocks and the newly implemented scoreboard system, it is perfectly possible to create a game of capture the flag in vanilla minecraft.

The unofficial editions of Capture the Flag have developed diverse ideas of the server type itself. Some servers have a default kit that you can't change, and some have multiple kits for different skills in combat. Some keep a record of kills, deaths, and captures. Some you have to physically destroy a block considered the flag, while others have the flags sitting as a dropped item on a pedestal that never disappears, which a person on the opposing team must pick up. But one aspect that is shared in almost all of the CTF servers is that you must take the flag back to your own team's flag or base to have it captured. Other than that, there is the aspect of maps. Some servers only have one map, while others have multiple maps that you can choose from through a lobby with portals, or just randomly selected after a match ends.

One way to build one (see also: Tutorials: Building a Metropolis): Have a 41 by 20 area split in the middle with a wall using pistons. Add 2 chests with 3 stacks of 20 arrows. Also have 3 bows. Have 2 trapped chests with your "flag". If someone is shot, they are out. Have a dispenser that shoots fireworks connecting to both trapped chests. The fireworks should be different. This lets people know who won. To make this, you'll need some redstone knowledge. You'll need: 20 wool, 2 dispensers, 20 pistons, 4 trapped chests, 4 chests, and a lot of redstone.

History
Capture the Flag was initially mentioned in the Minecraft prerelease announcement.

As mentioned at MineCon 2011, Capture the Flag will first be available for the Xbox 360 Edition before the PC version or Pocket Edition, although it is unsaid that it will ever be available in Pocket Edition.

Capture the flag is a gamemode, that has been mentioned by Notch, but not added into the game. It has 2 teams, who try and steal the opponents flag from in their base. Some servers have created this, with plugins and redstone. Jeb said he may add flags, so capture the flag may be coming out soon.

Teams
In capture the flag, there are two teams, normally red and blue, and on servers, the flags are normally "crafted" out of red and blue wool. As the scoreboard system has teams, that may be something to get closer to capture the flag.

How the game works
Capture the flag is a PvP game, with two teams. You try and steal the other team's flag, and return it to your flag. If you are successful, you win. If the other teams captures your flag and returns it to their base, you lose. Capture the flag is a multiplayer game, so you will need to know the ip for a server with this game on it. You could even host capture the flag games on your own server if you have one, and you want to.

How it can work with scoreboards
With a scoreboard you can build your own game of capture the flag, and when you capture the other teams flag, and take it back to your base, you can have a hopper, you throw the flag into it, and it goes into another hopper with loads of the other teams flags in (but it has to be the correct amount) then attach it to a redstone comparator, so when you throw another flag in, it powers the redstone comparator, next to a redstone repeater, and then just attach a redstone wire, connected to a command block with this command: /scoreboard players add @a[team=blue] flag 1 (for team "blue" if the objective checking if they have the flag called "flag." It is a little complicated, so you may need some redstone skills for it to work. If you have a team called red, and they win, the command would be: /scoreboard players add @a[team=red] flag 1