Cheats

Cheats mode is a feature avaible in 12w16a. When active, you can press the chat key and "chat". You can also do some commands such as /gamemode or /time set.

Cheats
/Gamemode 1/0 (Switch to Creative/survival)

/time set "time" (Sets time)

/give "item id" (Gives Item/block)

/xp "number" (Gives XP)

/kill (Kills yourself instantly)

/toggledownfall (Toggle rain/snow)

Trivia
You can't do server related commands such as /kick or /stop.