Chat Censor is a server-side mod that allows server owners to set a list of words to be censored (it includes some defaults), and users will see the middle letters of the words replaced with asterisks in the chat. In addition, users can individually decide if they wish to disable this censor. This uses the command /togglecensor, which is also configured to work with Sponge-based and Forge-based permission systems using the "command.togglecensor" permission. Again, this is a server-side mod, clients do not need to have this installed.
License: GNU General Public License v3.0