Riffle has been announced on the Mahout mailing list.
Riffle is a lightweight Java library for executing collections of dependent processes as a single process. It is Apache licensed so it can be included in non-GPL compatible projects.
The next major version of Cascading (1.2) will support the Riffle annotations so that projects like Mahout and Pig can participate in a Cascading Cascade execution.
Riffle can be found on its GitHub project page.