Fabrication is a rapid application development extension for PureMVC. It is built on top of PureMVC multicore. However you do not need to implement things specific to the multicore like multiton keys and such. Instead you extend classes like FlexApplication, FlashApplication etc. These provide the default implementations of all the multicore requirements.
From the pov of Fabrication the only conceptual difference between a standard and multicore PureMVC application is the use of onRegister in your mediators instead of putting the code in the constructor of the mediator. And since it is built on top of multicore, you would use classes from the multicore package.
You can find more details about the Features[1] and Documentation[2] in the links below.
peace,
darshan
[1] :
http://code.google.com/p/fabrication/wiki/Features[2] :
http://code.google.com/p/fabrication/w/list