How do application developers (on facebook) make money?

[Mr C]

I wonder how.

[shadowfox952]

The same way 90% of websites do it: Advertisements. Companies want to promote a product, they want to do it where a lot of people will see it, and they're willing to pay for it.

[facebook]

He is absolutely right. If a application developer can create something, (like scrabulous*) that is a quality product and can attract thousands or hundreds of thousands of users everyday, then companies will want to have their little 2 inch ad right where everyone who goes to take a turn in their scrabble match can see it. And it works!
Another way they make money is if the offer a product themselves of which the application is just a limited version or if the sell something else. ie Jetman** themed apparel is sold through the Jetman application page.

* Scrabble game for facebook
** Highly popular arcade type game on facebook