Final Fantasy XI but haven't been back in some time, you've missed a lot of updates. The game's run for 13 years now, after all; whenever you stopped playing, it's likely a lot of new content awaits you. And if you've got the hankering to check back in and see if it's how you remember, you can do so for a week. Completely free.
Until September 17th, former players can log in for free and explore all of the content available in the game. Players will need to transfer their old PlayOnline IDs to Square-Enix IDs if they have not done so already. A promotional video has also been released, detailing some of the changes made to the game for its current incarnation. So if you've got a hankering to step back into the world of Vana'diel, now might be the time to do so.