Square Enix has revealed that Final Fantasy III has released on Steam as of today:

SQUARE ENIX, Inc., the publisher of SQUARE ENIX® interactive entertainment products in the Americas, announced FINAL FANTASY® III, one of the most beloved games from the franchise, is available on Steam today. Now available on Steam, FINAL FANTASY III has been optimized for PC gaming with new and improved 3D visuals and story sequences. The game also includes Steam Trading Cards and Achievements and new visual designs for the Job Mastery Cards.FINAL FANTASY III was a hallmark of innovation for the entire series.  It introduced the job system that lets characters change classes at any time to the ability to summon powerful creatures. First released in Japan in 1990, FINAL FANTASY III was the first title in the series to become a million-seller.