McMMO Parties are a great way to go mining with a group, running through a dungeon (possible idea for the future?) with some friends, or anything of that nature where a group of people needs to communicate amongst themselves.
Commands: <required> [optional]
/party : displays information about your current party, if applicable.
/party join <playername> [password] : joins that player's party, if it's unlocked. Password may not be required.
/party create <partyname> [password] : creates a party with given password.
/party disband : disbands current party.
/party quit : leaves current party.
/party invite <playername> : invites that player.
/party leader <playername> : transfers leadership of that party.
/party password <password> : changes party password to given password.
/party lock : locks the party; you need an invite to get in.
/party unlock : unlocks the party; you can join with /party join.
/ptp <party member> : provides an alternative to /tpa, specifically for party members. Great on faction servers, or servers where /tpa is restricted. I don't see what you can really do with it here, but hey, you never know.
/pc : toggles party chat.
/pc (hello!) : sends given string to party chat.
/party itemshare <NONE;EQUAL;RANDOM> : EQUAL splits all goods evenly among party members; random obviously doles them out randomly.
/party itemshare <loot;mining;herbalism;woodcutting> <true;false> : enables or disables sharing of certain types of items.
/party expshare <none;equal> : splits McMMO XP among members.