***Update 2: My apps have been removed from facebook so I'm not earning anything anymore and that combined with the complete lack of updates from the company, non existent customer service, etc. I have to assume they've completely gone out of business.***
AppBank is a site that lets you make apps for facebook. It's pretty easy to use. You just sign up for the site, add their app to your facebook account, and that's pretty much it. You don't have to know anything about programming because they have app templates that you can use. Some examples of the types of apps you can make include name decoding apps, quizzes, games (the kind where you have to "hit" your opponent within a certain amount of days or they win), gifting apps, and quotes.
Once you publish your app, you have to get at least 10 people to use it (should be pretty easy, this is facebook we're talking about after all) and then you can submit it to the facebook app directory. The app will show advertisements each time it's used and that is how you make money.
So how much money can you make? I have not been paid by AppBank yet (you have to have $5 in your account to get paid). I've made 4 apps so far (a Criminal Minds trivia quiz, A movie trivia quiz, a music trivia quiz, and a "funny faces" gifting app). I haven't done a whole lot to promote them (other than bugging a few of my friends to take my quizzes lol). I started using AppBank in October 2010 and so far I'm only up to about $1.73. I'm earning anywhere between $0.02-$0.07 a day. That isn't much, but considering that it's completely passive income (except for actually making the apps, which only takes a few minutes) and that I have only made 4 apps so far, I'm pretty happy about it.
I'm pretty excited about AppBank and I plan on making more quizzes and apps as soon as I can. I think this could be a great way to make some extra money (especially if you had an idea that really caught on).