There's no such thing in XI, although there are systems that resemble it.
By the core guildleves are like quests in other MMO's. There's few differences though.
Each leve has 5 difficulties, with different rewards. Solo being the easiest and 10+ member leve being the hardest.
Leves also have time limits, varying from 15mins to days, depending on the scope of the leve.
You can also (supposedly) mix up your leves to make up longer campaigns.
There's around 25 type of leves to do. Cafters have their own leves, gatherers (like Miner) have their own too.
Boss fights are probably included too, but when it comes to storyline there are "Class Quests" that advance the storyline and are separate from Guildleves.
Just to tag on Heksars questions so I don't have to make another thread, I have a couple questions also.
1. FFXI quests didn't give exp rewards just gil and loot, (at least back when I still played). For some reason I liked that. Every mmo I've played since the quest rewards all gave exp. Do Guildleves give exp also and if so does it increase with the difficulty?
2. Are the Guildleves repeatable? What I'm asking is if I decide to solo a guildleve for whatever reason and get my reward for completing said quest will I be able to go back and do this quest at a harder difficulty with a full party for a better reward at a later date? Does completing the Guildleve only allow you to participate in the quest to help a link member for example but not let you get that guildleve reward again for participating at this new difficulty level? I'm sure there are repeatable quest like all mmo's but are they all like that?
3. From what's been seen in the Alpha are any of the Guildleve level restricted? I know I know. No levels in this game, but what I'm asking is can a lowbie get 8 high lvl players to do a max difficulty guildleve for him?
I'm fully aware that the game is still in Alpha and many of these questions and answers might be very different on release. But as it stands now how are the current guildleves working based on my questions? thanks in advance.