I have looked at some tutorials that claim you can rig in Unity, however in these tutorials the person doing the tutorial then uses pre-rigged Mixamo characters or mechanim.
Is there a way of getting any object (even a sphere) and rigging it? I have Blender and might use it to rig, but I much prefer the interface of Unity.
Itās been nearly a week without a response. Am I to assume that it isnāt possible?
I assume you mean āskinningā by assigning vertice weights to bones, etcā¦ which is indeed not possible. You can only import and customize which bones are āonā (basically) with the imported rig and Mecanim sprinkles magical dust to make it retarget and adjust the model to work on the skeleton. Thereās more features of course, but nothing like traditional rigging in that sense.
Very far down on the roadmap is in-editor IK building, but not any time soon.
Thank you for the feedback - I can stop holding onto the idea that I donāt have to teach myself how to use Blender (I find its key combinations and interface confusing).
kittik - you should download a trial version of zbrush and play with it for a couple days. You will find Blender refreshingly simple and intuitive after experiencing zbrush up close. 
You can change the key combination presets to something more sane( maya, 3ds max) in the welcome screen. Sadly, I donāt think thereās any other options for doing 3d skinning/rigging for free.