A picture can be worth a thousands words. You can find many interesting and self-explanatory pictures here:
In a nutshell: Spinach is not a program, but an open source library; it's something for programmers, not for end users. The language is, once again, Matlab. When the language is Matlab, usually that the programmer and the end user are the same person.
The purpose of Spinach is, once again, to simulate NMR experiments and spectra, of all kinds. With this latest arrival, I am even more convinced that the vast majority of NMR software belongs to the class of simulation software. The mole of published material (in the sense that you can find an article in literature) is inversely proportional to the number of users. It is a fascinating field nonetheless. You can freely download Spinach and read it. Installing it is a different story.