A lot of people ask me about Objective-C programming language because it seems to be difficult to learn, my answer is "For Sure!". For those who works for years in low-level applications (like C, Cobol and Assembly), it's fine but those who works with high-level applications (like PHP and Flash) it's very hard to go into Objective-C.
Because of that, some people or companies made frameworks to be easier for us to develop applications. Apple did not like some frameworks and was rejecting apps made with them, but some days ago they turned back and made a lot of people happy (hello Adobe!).
So, I will talk about some frameworks that you can find out there. These are not ALL frameworks, if you google it, you'll find tons of frameworks.
1 - Cocos2d
I've talked about it on the other post about game basics. Cocos2d uses XCode and have to be programmed in Objective-C but have a lot of APIs that make our lifes easier to develop games. It have 100% integration with iOS sdk but unfortunately, you still have to leran Objective-C.
Image taken from: http://www.geekology.co.za/blog/wp-content/uploads/2009/07/xcode-objectivec-iphone-5.jpg
2 - GameSalad
This is most easier of all! GameSalad is "Game creation for the rest of us" because it's so easy that you don't need to know any programming language to build games. Of course is better if you know any programming language because of the logic knowleadge but you can still build something without that. The problem is that you can't do a lot of things like use arrays, sql, text functions (ex: substring) and play movies. GS have a pro version but it only gives you directly support, no gamesalad splash screen, iADs and url request. This is NOT worth to pay $2000 while the standard is $99. GS is good but have a lot of thing to improve.
1 Year Subscription Price: $99 - $1999 (pro version)
Image taken from: http://www.gamesalad.com/
3 - Unity 3D
Purchase Price: $300 - $1200 (pro version)
Image taken from: http://blog.webcore.com.br/wp-content/uploads/2008/09/tsc01.jpg
4 - Corona
By the time of this post, Corona was in beta version and price. It will be updated soon and the subscription will be more expensive, but let's talk abou the SDK. Corona is a sdk that uses Lua programming language (made in Brazil) that have a lot of power and can be learned very quickly (especially if you are a Flash developer). Corona doesn't have an editor, you have to build the code in any text editor but it have an iPhone simulator to run the games. A great thing about Corona is that the same code can build games for iOS and Android, it's very easy to do it. Corona have powerfull API's with integration to Facebook and OpenFeint. After GameSalad, Corona is the easier framework to learn but it's powerful and have better performance.
1 Year Subscription Price: $99
Image taken from: http://www.burtonsmediagroup.com/blog/wp-content/uploads/2010/06/Screen-shot-2010-06-21-at-2.36.06-AM.png
---- Conclusion ----
After tried all of these frameworks, I can say that GameSalad is excelent for begginers but if you want same pro functions, is better to go to the others. Unity is incredible but it's the better choice only if you want 3D games. Cocos2D is Objective-C, so for me is the worst choice you can take! (nobody is here to reinvent the wheel) Well, the last but not least is Corona that I'm with great expectations with the final version. Corona is simple, fast and have great built-in functions. Unfortunately, some of my first tests doesn't worked well but I hope it happened because it's a beta version. For now, I'll do my ideas on GameSalad and later implement on Corona.