Ryan Roberts covers how to create bendy limbs and their parts with Bifrost in Maya.
Check out this two-part tutorial from The Rigging Space channel (Ryan Roberts). Ryan shows how to create part of a bendy limb using a curve with a Bifrost Graph in Maya.
The tutorial covers some conversion options when translating a curve into a Bifrost Strand. Ryan also reviews simple matrix math and shows how to get local matrix values from world matrix values.
Part two covers creating the elbow control for the bendy limb. Ryan uses Bifrost to counter-rotate the assigned controllers, so it always appears to be angled between the two limb joints.
More on Rigging With Bifrost.
Also, on transformations and rigging, check out this Bifrost tutorial from Jason Brown, who covers an easy way to move an object or its corresponding field when working in the graph. Visit that tutorial here.
Check out this open-source project started by Daniel Lindsey, a Media and art Pipeline Manager Senior at Walt Disney Imagineering, which offers a rigging toolset based in Bifrost. Visit that post here.