This plugin allows you to form groups of people who restrict each other from equipping certain items.
Once a player equips an item, his Group ID that he's selected, his username, and the item are stored in a database, and then nobody else in that group will be allowed to equip that item.
There's also a setting to exclude any items needed to complete quests from being restricted (e.g. Excalibur, Mourner Outfit, etc.)
In the future, I plan to update this to have options for excluding various tiers of clue scroll required items, as well.