There is very annoying phenomenon on the iTunes app store. I don't know what to call this type of app, so I am calling them cluster apps. Let me give you some examples.

miArtPak

There are no less than 9 miArtPak apps. These apps provides artists with a way of distributing their artwork to the iPhone. Each app is for an individual artist. Some are free some costs $0.99. The artwork is beautiful though.

GP apps

Then we have a small company called GP apps. They have:

5 apps called DialTextEmail "x".
11 apps called GroupNotes "x".
10 apps called Note to "x".
18 apps called TapDialer "x"

with x = {Girlfriend, boss, best friend, mom, coworker, etc. }

Judging from the screenshots, descriptions, and titles they all do the same thing.

Obscure Clocks

Then we have from the same developer:

Ball, Binary, Borg, Braille, Elvish, Hebrew, Khmer, Klingon, Roman, Romulan, Sinhala, Tamil, and Thai Clocks.

Most of these developers change the colors of the icons and the publish the app under a different name.

Why?
Presumably developers do this because they want a larger surface area of the iTunes store and making sure that people can find the apps. It is also no secret that every time you submit an app and it is just out on the app-store you will get a boost in sales. From my experience you can sell between 30 and 100 the first couple of days. If you have 18 apps of the same type, you could hope to make 18 times as much. I am also guessing they do it because they want you to buy a whole series of apps. Instead of having just a free and a paid version, you can buy the pieces you want. Like Vint B&W, Vint Red, and Vint green. They all make "vintage" looking photos, but with a slightly different tint.

Does it work?
... hopefully not. It is not a pretty business model. You are complicating the life of your customers since flooding the app store with identical apps, makes it tougher for them to find what they really want. You are also stressing the Apple review team with a large pile of identical apps. It is also slightly false marketing, to be marketing similar apps as if they are different.

Enough about the moral aspects though. Let's look at the numbers. I have used (http://www.apptism.com/) to get rankings of the apps. Rankings are based on category, so we have to consider each individual category by itself.

Let's begin with photography. My own Thanksgiving Turkeynizer has been downloaded less than 1000 times total, 400 of those were actual sales (It was free for a few days), and I am currently selling about 1 per week. The Thanksgiving Turkeynizer has rank 212.

The non-free versions of miArtPak are all in the 200-300 ranking area. So they are each selling worse than the Turkeynizer.

Vint apps are ranking 36, 97, and 196. Pretty, pretty good!

The clock apps are in a different category (Utilities): Klingon clock seems to be the best with a rank of 1078. My guess is that he is selling 1 per week at most.

Then there are the "Note to" apps. I notices these about 1 week ago, but when I tried to search for them on the app-store they were pretty hard to find (even searching for "Note to"), so I am guessing the whole surface area strategy does not hold. Anyway, Note to boss (564), Note to mom (528), Note to myself (Portrait version), (ranking 304) [portrait, wtf!], Tap dialer boss (531). Basically, we are generally in the 500 ranking area.

So how much are they selling? Probably not much. I don't think GP-apps' strategy works, and I am pretty sure that the clocks from the same developer would actually sell well if it was just one single app. Customers who wants a weird clock, would be super happy if they could have a new weird clock each day, but having to buy all 10 of them is just annoying from a customer point of view.

The Vint app was the first I noticed of this type, and I am surprised that it seems to work for him. From my own experience an app with rank of 36 sells at least 4x as much as one with rank 100 and at least 10x as much one with rank 200. So my guess is that at least 80% of his income comes from Vint B&W. Why not just combine the three apps into one and perhaps climb to rank 25?

Annoying
These apps are really annoying. They take up space in the app-store and they give it a bad reputation. Based on the rankings, people also don't care about them. They all try to target specific individuals either with the name or content. A large part of making it on the app store is to gain popularity, and selling a small number of apps to individuals will not gain anything from a popularity point of view. Instead you are risking a sure drop into darkness after that initial boost.

Guilty!
I must admit that I have three apps out there with similar concepts Halloween Pumpknizer, Thanksgiving Turkeynizer, and XmasizeMe. I am currently considering combining them into one app for the next big season, but to be fair, the apps are really quite different although they are based on the same concept and code. In any case, I am now convinced that making just one app from the beginning with seasonal updates would have been a far better strategy, because it would have made customers so much more happy about it.