If I understand correctly, the Raspberry Pi does not run OS X. Is there a way to get OS X run on the Raspberry Pi?
Do other boards like the Raspberry Pi exist that can run OS X?
Yes, you do understand correctly - Raspberry Pi does not run OS X. OSX is compiled for Intel chips; the Pi uses ARM chips.
You are confusing OS X and Linux. Both are based on an old operating system called Unix, which is pretty much the mother of all OS's. I may be wrong, but even Windows has a bit of Unix mixed in.
What is OS X?
OS X is a proprietary OS used and created by Apple Inc. It is based off of Unix, NextStep, and the original Mac OS. Unless you do some hacking (not the illegal kind), you will be unable to run it on any hardware other than one bought from Apple. If you are interested in creating a non-Apple system that can run OSX, you should go to the Hackintosh Website. Lastly, I seriously doubt that a single (and simple) board computer like the Pi (even if it uses intel) will be able to handle a large, modern OS such as OSX.
What is Linux?
"Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution." - Wikipedia This means that anyone can modify Linux as the kernel is available freely (both in free food and free speech.) Unlike OSX, there are many different "forks" or "flavors" of Linux. Wheezy is based off of Debian, but there are also other forms such as Ubuntu, and Arch Linux. Lastly, unlike Windows and Mac OSX, Linux is easily customizable. It can look like a Mac, it can become a CLI interface, and can do a myriad of other things. There are versions of Linux that run on both ARM chips and Intel chips.
I hope that I answered your question fully. If you have any more concerns, feel free to leave me a note in the comments.
While the iPhone certainly proves that OSX can run on a similar chip like the one on the Raspberry Pi, there are some catches.
First and most importantly, OSX is propriety, and is only licensed to run on Apple issued hardware.
However, at the core of OSX is Darwin, a Unix Variant derived from NextStep, BSD, and likely some other Open Source projects. Darwin could be configured to be recompiled on other Chip Architectures. I believe what is currently supported are Intel based architectures and 32 Bit ARM (as on the iPhone and the Raspberry).
But why the hassle ... Debian runs fine ... try Raspbian.