Here are fairly recent versions of the Compacts of Agora's Public Organizations:
Groups are Organizations of Players who (supposedly) share the same views towards Agora. Each Player may belong to exactly one Group, or be unaffiliated. Each Group can cast one Vote per Proposal. For more info on Groups, check out the Rule Category "Groups and Contests", specifically Rules 766, 721, 719, 718, and 716.
Contests are Subgames of Agora. Each Contest has a Contestmaster, who is the moderator of that subgame, and Contestants, who are those who actually play the subgame. Players can be in multiple Contests. For more info on Contests, check out the Rule Category "Groups and Contests", specifically Rules 1446 and 1539.
Hoards are technically Contests, and follow all the Rules for Contests (see above). But they were formed specifically to hold Currencies for their "Contestmasters". The reason this was useful was that at one time, Points could be transferred, and so these Hoarders transferred their Currencies to the Hoards, to keep them between games (when Points are normally reset to 0).