A free Blender add-on for layering and painting BSDF materials.
Poser 12 uses Principled BSDF now, so presumably it wouldn’t be too difficult for this Blender add-on to have an “Output straight to a Poser material file” button? I believe the setups are identical to those in Blender, except for being ‘mirror-backwards’ in their direction of node-flow.