MyFaces, an open-source, non-Sun JSF implementation is available at
the open-source Apache website page myfaces.apache.org. An earlier
version of ADF Faces (10.1.3) was donated to the public domain to
kick off the Trinidad project of MyFaces.
Not open source in the sense that you can just download, modify and share the ADF code.
However, the source code for ADF is available for all customers with a current support contract. You open a Service Request with Oracle support, fill in some paperwork (accepting that you can't publish it, among other things) and then Oracle Support makes the ADF source code availabel to you.