Mixamo is described as 'Animated 3D characters. No 3D knowledge required. Rapidly create, rig and animate unique characters for design projects' and is a 3D Animator in the Photos & Graphics category. There are six alternatives to Mixamo, not only websites but also apps for a variety of platforms, including Windows, Mac, Unity and SaaS. The best alternative is MakeHuman, which is both free and Open Source. Other great sites and apps similar to Mixamo are DAZ 3D (Freemium), Poser (Paid), Xnalara (Free) and RigModels.com (Free Personal).
MakeHuman is an interactive modelling tool for creating realistic 3D human characters. These models can be exported to several computer graphics and animation platforms including Blender, Unity 3D, Unreal Engine, OpenSim and Second Life.