Bukkit

Commands:

/silence - Show information on command usage
/silence <player> - Query silenced status of <player>.
/silence <player> {ON|OFF|<duration>} - Set or remove a silencing.
/silenceall - Query status of global silencing.
/silenceall {ON|OFF|<duration>} - Set or remove global silencing.
/ignore <player> - Query silenced status of <player>.
/ignore <player> {ON|OFF|<duration>} - Set or remove a silencing.

Duration formats:
1d2h3m4s = 1 day, 2 hours, 3 minutes, 4 seconds. Each term is optional. Eg. 1d5s is 1 day 5 seconds.
1:2:3:4 = 1 day, 2 hours, 3 minutes, 4 seconds. Preceding terms are optional. Eg. 1:23 is 1 minute 23 seconds.
3600 = 3600 seconds, or 1 hour.

Permissions:

silence.query - Allow user to query silence status of players.
silence.modify - Allow user to set/remove a silencing.
silence.queryall - Allow user to query silence status of global silencing.
silence.modifyall - Allow user to set/remove a global silencing.
silence.silenceall.ignore - User may ignore the global silencing and speak.