Microtransactions. "Micro." As in, very small bits of money—a dollar here, a dollar there—exchanged for comparably small in-game items: A new hat, perhaps, or some healing potions. But boy, it sure adds up. Riot Games earned $624 million from League of Legends last year, and that was only good enough for second place on the top-ten free-to-play earnings list. In 2014, however, it's shot to number one, and is poised to be the first to break $1 billion in microtransaction revenues.

League of Legends pulled in an estimated $964 million between January and September of this year, according to SuperData research (via VentureBeat), making the magical $1 billion mark almost a sure thing. And it's not alone: Last year's first-place finisher, the military FPS CrossFire, is at $897 million, Nexon's Dungeon Fighter Online is sitting at $891 million, and World of Warcraft has brought in $728 million. All them have a good shot at making it over the hump.

Also noteworthy is just how badly League of Legends is trouncing the other big free-to-play games in North American, Dota 2 and Hearthstone. Both made the list, but way, way back in the pack: Dota 2 is at number nine with $136 million in revenues, while Hearthstone brought up the rear with $114 million. I'm not going to shed too many tears for either of them, but it's a remarkable gap between them.

The World of Warcraft situation is interesting as well. Subscription numbers have slid dramatically over the past several years (although they recently enjoyed a bounce thanks to the launch of Warlords of Draenor), but the spending on in-game items, which is all these numbers take into account—no subscription revenues, in other words—is way up: Its nine-month total is more than triple the $213 million it earned in all of 2013.

In a similar light, Hearthstone may be doing better than it appears, because the figures are PC-only and thus don't account for mobile spending. That still wouldn't be enough to get it near LoL, but it might move it up a few places in the list.