XPCKit
Steve Streza (via Gus Mueller):
XPCKit is a Cocoa library for wrapping the XPC C APIs in a handy object-oriented model. It is merely meant as an object-oriented wrapper for the C library, and does not attempt to layer any additional semantics on top.
I get why Apple wanted to use a different set of types for IPC, but I bet lots of people will be writing their own boxing and unboxing code for xpc_object_t and Cocoa property list types.
