Blender
Blender-Logo

Blender:

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, it us greatly used among VRChat users because of the free to use nature.
The program is a powerful avatar and model creation tool you can do a lot with this program, from setting up your model for use in world creation in Unity to creating an armature for moving/deforming the models or avatars in realtime, there is a great amount of Videos and Addons that help you through the journey to become a better artist, there will be links to the best tutorials we can find and get started guides here, we hope you will enjoy what VRChat has and will become from the use of free tools like this.
"Live Long and Prosper"

Learning Sources:

  • Blender Stack Exchange - This site answers questions specific about Blender, this is a good site if you are stuck with something or cannot find a way to deal with a problem you have, the site does cover more of the animation and scene setup in Blender but there is quite a few problems solved through searching on this site.

Blender Specific Youtube Channels:

  • Blender Guru - One of the biggest Blender channels for learning Blender, many guides and videos crafting an scenes, rooms, subway and many other areas from scratch.
  • BlenderBinge - A great channel for teaching Blender from A to Z
  • CG Cookie - Small team making many guides and tutorials for Blender
  • CG Boost - A channel about Blender and tips and tricks for making beautiful 3D Art.
  • Darrin Lile - Series to show workflow for modeling, texturing, rigging, weight painting and animating a model from scratch.

Add-ons:

  • Cats Blender Plugin - A Good Addon for Blender when making or editing Avatars for VRChat before importing it too Unity.
  • Material Combiner Blender Addon - Used by cats for auto-atlassing and also has features for creating atlasses of multi-texture materials (normals, etc).

Links:

Blender main page, you can download the software from here for free:
https://www.blender.org/

References: