Swigert - here's my take on the big picture. There are several languages and ways to use them on the Edison supported by Intel; C, C++, Javascript and Python. Other languages could be used, too, but these 4 have IDE's, libraries, examples, etc. on various Intel web pages.
C and C++ can be used with an interactive IDE (IoTDK) from your desktop. It has a cross compiler that compiles C and C++ programs and uploads them to the Edison. The Edison itself also has a compiler that can do this directly. The mraa-upm libraires let you control GPIO and sensors. IoT - Home | Intel® Developer Zone
Javascript can also be used interactively with the Edison from your desktop using Intel's XDK. Since Javascript is an interpreted language, no compiling is involved. The Edison has node.js on it, so you can run Javascript programs directly on the Edison. The mraa-upm libraires let you control GPIO and sensors. There are also other 3rd party libraries available like Cylon and Galileo-IO. Intel® XDK IoT Edition | Intel® Developer Zone
Python is handled a bit differently. Intel doesn't have an IDE for this, although you could use Eclipse with a Python plug-in. But since Python is already installed on the Edison, you can use your own editor on either your desktop or the Edison and then run Python programs directly on the Edison. Libraries have been built into Python on the Edison to support GPIO and various sensors. You can find Python examples at both of the above links.
While each of these are well supported within their own environment (well maybe not Python so much), in my opinion, Intel could do a bit better bringing all this together under one umbrella, at least for those new to the Edison.
In any case, from my experience using several other popular boards, Intel's IoTDK and XDK are vastly superior to what those other board builders provide for their products.
Intel guys - feel free to correct or add.