Bukkit

The commands are as follows.

/jail a [player] (time) : Adds specified player to jail for the optional time.
/jail add [player] (time) : Same as above.

/jail r [player] : Releases the specified player.
/jail release [player] : Same as above.

/jail set jail : Sets the jail teleport coordinates for players that get thrown in jail.
/jail set chat (on|off) : Toggles chat for detainees or turns it on or off, if specified.
/jail set leave (teleport|command|both) : Sets which option to use when releasing a player (teleport them out, use a command, or both).  (since v0.3)
/jail set leavetp : Sets your position as the jail release point, if use is set to both or teleport. (since v0.3)
/jail set leavecmd [command1](;command2) : Sets the command(s) executed by the player when released if use is set to both or command. (since v0.3-previously was /jail set leave)
/jail set broadcast (on|off) : Toggles the jailed/released broadcast or turns it on or off, if specified. (since v0.2)
/jail set griefingextends (on|off) : Toggles the block breaking/placing time extender or turns it on or off, if specified. (since v0.2)
/jail set griefing (on|off) : An alias for above. (since v0.2)
/jail set grief (on|off) : Another alias for the above 2. (since v0.2)

/jail info (player) : Gives the time left on a sentence for yourself or if the person has permission the specified player.
/jail i (player) : Exact same as above. (since v0.2)

Time is specified as a number and character. Multiple arguments are separated by , (a comma).
The appropriate characters are:
m for minute
h for hour
d for day
w for week
y for year

For example: /jail add (player) 5m,1h

Player will try to be matched to someone who is online, if not then it'll need to be exact for offline players.