Actually what i was thinking was more or less having the program "auto-convert" the rigging. Say for example you export M4 into Blender, but Blender does not support Poser's rigging system.  So during the export the program would  give it's best approximation of M4's rigging using Blender's rigging instead. I guess you could always make adjustments  if needed.

Wouldn't the creator of said app need to get permission from each company whose rigging s/he plans to implement? Doesn't sound like an easy task.

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Daz, Blender, Affinity, Substance, Unity, Python, C#