If it's been a while since you last checked up on Final Fantasy 14 but have been craving a return to Eorzea, good news! From today, lapsed players who have been away for more than 30 days can return for free, but only for six days. That's not a lot of time for a huge MMO, but it should be enough for you to decide if you want to stick around.
The free login campaign will run until August 16, but even if you start playing today you will still only get six days. It's a bit weird that it's timed instead of just letting all returning players enjoy the game until next Friday, but Final Fantasy 14 is a sometimes confusing game, so this tracks.
Once you've reinstalled the game and logged in, the free period will begin. Square Enix specifically mentions the launch of Shadowbringers being a reason to come back—although you'll still need to splash out if you want to play the excellent expansion.
As always, there's also the free trial for new players. It comes with a bunch of restrictions, but it lets you play up to level 35.