Greetings!
“Chiro UE4 Mannequin” is a new Open Source add-on for Blender, making skinning (aka rigging) with Mannequin armature simple and easy as a breeze.
A developer met an artist, and together we made the new addon. This is Open Source and free software (as in freedom). We’re happy to announce the first release and share it with you! The license is GPL3, so you’re free to share it too, by the way 
So, what does it do?
Skin humanoid meshes in Blender with Mannequin skeleton and export it correctly into FBX. Resulting Skeletal Meshes are compatible with Mannequin in Unreal Engine 4 either via retargeting with humanoid rig, or reusing Mannequin skeleton straightforwardly. Yes, that’s right, if your Character has the same proportions with Mannequin, it’s possible to reuse the Mannequin skeleton with no retargeting altogether!
Mixamo converter as a bonus.
The add-on has tools to convert Mixamo skeletons to Mannequin in just about 10 clicks.
Here are some examples of the add-on in action (with videos):
If you’re interested, here is the documentation.
GLHF!