Style Modules is a project begun but somewhat on the backburner for the moment. The initial concept and repo exists on the BP github account:
Github BP: style-modules
Further development has been progressed on my personal account to flesh out some further details:
Github hnla: style-modules
The intention for these modules is to provide a mechanism by which wider developers may contribute small libraries of code to style and manipulate (JS) elements within BP components, e.g. styling the list directories to display as panels in a grid system.
It was envisaged that this may be a good means of getting a wider involvement in providing custom code for BP and in getting a new set of developers involved engaged in providing this while not having to go to the somewhat more involved process of creating full blown plugins.
For the moment this project is on hold but the idea retains merit and is hoped to be revisited at a later date.