TalkArea

TalkArea is a mod that allows players to set a distance beyond which other players will no longer be able to hear them.
This mod is primarily intended for RP servers.

Its goal is to make in-game chats more like real-life conversations where only people close to you can hear you. This also allows for a certain level of privacy in chats without having to use /msg every time (and makes it suitable for conversations involving more than two players).

It is designed so that players can decide for themselves whether to enable it and set its range (use the /talkarea command in-game to get all the details), but it is possible to force it on all players on the server through the server config.

The mod must be installed on the server AND the client.