FATE

Rewards are decided based not on party, but individual performance

All players treated as "one large party" [so basically you just get flagged as "near enough to be evaluated for a reward, which also level-synchs you to the event level]

Level sync only works one-way: if you're above content level, you will be de-levelled, if you're below content level, nothing happens.

FATE types:
Notorious Monster
village/city invasion (example: bandits/thieves)
chocobo escort

No limit on how many people can participate in a FATE

They are thinking about a system that automatically creates an instance and moves the half of the people to a new one should the number of people reach a certain number
While this system is technologically possible, the cost is high, so they are planning to monitor the events in alpha&beta to decide if it's really needed.

* * * * * * *

With the exception of the Overflow Instance that occurs during a FATE, this feature of ARR is one I'm most excited about. I got a taste of it in GW2 and it was the best thing I liked about it. What I liked most about it was that it just wasn't one FATE, it was several strung together. NPCs participated in the fights that lasted a while and involved wave after wave of mobs.

Now some folk say that GW2 made people level up too fast, but I submit that if you are playing the game and the game is throwing mobs at you for about 45 minutes you should level. XD And having events like this negates the idea of a "boring grind". If your "camp" is a FATE, you're having fun while you're grinding mobs and levels.