Being an independent app developer is a tall order these days. They have to battle multiple APIs, changing SDKs and a mountain of competition, all for the very slim chances of just being noticed (much less successful).

So when apps manage to rise to the top of the heap, it's a huge accomplishment — one that can turn their developers into millionaires. The obvious example is Angry Birds: Rovio made such a huge killing from the apps and the merchandising, that it's trying to take over the world now. It may even succeed, what with A.B.-themed credit cards, amusement parks, movies and more on the way.

So who are the millionaires on the app scene now (that is, aside from Angry Birds)? There are quite a few, but a few noteworthy ones — plus some rising stars — include:

Draw Something: $180 million

When Zynga bought OMGPOP, it plunked down $180 million dollars for it, all for the pleasure of having the enormously popular Pictionaryesque app Draw Something on its roster. That's amazing considering that OMGPOP was going down the tubes fast when the app was released, on February 1. Just six weeks later, the acquisition was finalized, clinching the fact that Draw Something basically saved the company's butt.

iFart: ~2 million

Really? A fart app? Absolutely. (Never underestimate the people's need to mimic the sounds of bodily functions with tech.) Maybe it was because Joel Comm got in the gross apps game early on, in December 2008, but whatever the reason, iFart seemed to enchant the gas-enthralled masses. At $0.99, it hit almost 114,000 downloads in its first two weeks, yielding about $79,000 in profit. Much imitated, but quite never duplicated, iFart's popularity only grew from there. (Apparently, even George Clooney admits to fake farting with it.) It's a simple app with one primary function, and basically no updates since its release, and yet, it technically qualifies for this list. And that's no hot air.

Instagram: $1 billion

We need a new category for this one. Instagram looks at the millionaires list, and just laughs at it, as the photo editing and sharing app was famously picked up for $1 billion dollars by Facebook. What most people don't know is that it was created by a 28-year-old — Google and Twitter veteran Kevin Systrom — who began this project under the name Burbn. It launched in October 2010, and has gained an enormous fanbase since then, for reasons that are absolutely obvious: It's super simple to use, and has awesome filters and robust sharing capabilities. (Fingers-crossed that it remains that way under Facebook.)

Fruit Ninja: ~3 million (?)

It first landed on the iPhone, but now HalfBrick Studios' Fruit Ninja is on iOS, Android and WinPho devices everywhere. The fruit-slicing game has even hit the XBOX Kinect now too. That makes it tough to suss out the actual hard numbers, but this Aussie import's popularity — and ubiquity — across the platforms makes its estimated 3 million dollar figure look pretty conservative. In fact, total sales across all platforms lapped 20 million at this time last year. And total, it has hit 300 million downloads. That's about 1.5 trillion pieces of virtual fruit sliced in two years! HalfBrick's Phil Larsen told the Courier Mail, Fruit Ninja is its very first iPhone game — totally self-published, self-created and self-funded. Larsen said HalfBrick — which went from three people to 60 in its 11-year existence — went into the mobile game app space (from DS and PSP game development) because it saw a shift happening in the industry. No cartridges or discs necessary, "you can have your games online at any time."

Minecraft: 33+ million

This is a no-brainer. When Markus "Notch" Persson created Minecraft, he never expected the sandbox-style game to be the massive success it has turned out to be, having generated 33+ million dollars so far. Co-founder of Mojang, Persson just wanted it to make enough to pay the bills to develop his next game, whatever it would've been. Next thing you know, a full-on Minecraft culture has taken hold of kids, parents, geeks and artists alike. And when the day arrives when it starts to lose some of its epic appeal, Persson plans to let the source code out so other people can take further the game.

iShoot: ~$2 million
There are several things I like about iShoot: It's an elegantly simple shooting game. It has a nostalgia factor, since it almost plays like a classic PC game. And its developer, Ethan Nicholas, is a self-taught coder. (Sure, he's an engineer, but he was no developer. This was his first app using Objective-C, and on an ancient, original MacBook, no less!) Early on he managed to hit $37,000 in one day, and his 2009 sales figures reached $800,000 just by April.

Of course, not all the residents of App Street are living the high life. But for aspiring developers, this ought to be pretty inspiring. It's like the new American dream, rebooted for the modern era. Not everyone needs to be backed by a major company to make it big. Sometimes all you need is a good idea (or, in the case of iFart, a weirdly compelling idea), some chutzpah and a lot of tenacity, and you too might find your code lined in gold. Do you have a favorite app that deserves a mention, whether due to its success or just plain awesomeness? Be sure to give it a shout-out down below.

[via Chip Chick]