These are applications that allow you to design in 3D and export a file in a format Babylon.js can import.
Blender is the free and open source 3D creation suite. It supports the entirety of the 3D pipeline—modeling, rigging, animation, simulation, rendering, compositing and motion tracking, even video editing and game creation.
3DSMax is a commercial 3D design software for modelling, animation and rendering. There is a 30 day free trial period.
Unity is a commercial cross-platform game engine which is primarily used to develop video games and simulations for computers, consoles and mobile devices. There is free use option for beginners, students and hobbyist.
Cheetah3D is a commercial MacOS computer graphics program for 3D modelling, animation and rendering. The program is aimed at beginning and amateur 3D artists. A free demo version is available but this can neither ssave nor export files.
Blender
Blender tips
Blender - Installing the Babylon Exporter
3DSMax
3DSMax - Bones influences per vertex
Unity
Cheetah3D