Grothendieck, before he disappeared, was working on a manuscript called "Les Derivateurs", which detailed the theory of derivators.  Prof. Cisinski has done work with them as he mentioned in this [post](https://mathoverflow.net/questions/17425/homotopy-limits-over-fibered-categories/17463#17463).  However, most of his work is in French, and I was wondering if there are any typed up references in english (the nLab has written notes from a seminar, but that's it).  I intend to read the references in French later, but could someone explain or give a reference that explains in English the definition of a derivator and the motivation for them?