Auto-Rig Pro is an all-in-one solution to rig characters, retarget animations, and provide Fbx export for Unity and Unreal Engine. First coded for my own projects and needs, it has expanded drastically other the years with hundred of new features.
Position the reference bones so that they match your character proportions. To speed up this process, the smart tool will automatically try to find the body parts locations for you (bipeds only so far). Then, edit the result if needed (if your character is not a biped/ or for more accuracy), eventually place the facial bones and other extra limbs, and generate the final rig. Based on a non-destructive workflow, the armature remains easily editable anytime after the generation.