Capture the Flag

Capture the Flag is a multiplayer game mode that Notch mentioned would be added to Minecraft in the future.

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.

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. 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.

History
Capture the Flag initially mentioned in Minecraft prerelease announcement.

As mentioned at MineCon, 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.