Party List

The Party List is a widget similar to the Battle Window that displays the members of your character's party. It is used to keep track of their Party's members Health and Mana, which is visible isn't if the character isn't in your game window but nearby. 
One of its most important uses is keeping track of your party members stats even if you can't see them if there are too many effects appearing on your screen, for example. Similar to the Battle Window, you can also use runes on the Party List, which is very useful for using e.g. UH runes without having to aim on the game window, specially when the other player is moving. 
You can also use the Party List to assign the leadership of a Party to another player even if they are far away from you. Furthermore, you can filter the Party List by vocations and sort them by different values, allowing you to customize it to your needs.