MK is a set of common plumbing that different WSAPI applications and frameworks can use to do things like share a single authentication system, easily create inter-application links, and embed pieces of content created by different frameworks (mixing Orbit and Sputnik content in the same page, for example).

Look in the samples and test folders to see examples of the APIs as they are right now. To run these you need to install the two rockspecs in the rockspecs folders, which install MK and a branch of WSAPI which changes that MK needs (these changes are in a branch because thay can potentially break existing WSAPI applications).