3ds Max is a 3D computer graphics program for making 3D models, animations, etc. It can also be used to import models using MaxScripts.
3ds Max can be downloaded here. However, barring the free trial, 3ds Max requires the user to pay for a subscription in order to use it.
A list of MaxScripts that support model formats used in Sonic the Hedgehog 4: Episodes I and II.
The Sonic 4 Bonus Site is not associated with SEGA, Sonic Team, or Dimps.