What are some alternatives?
When comparing Strata Design 3D CX and Silo, you can also consider the following products
SelfCAD - SelfCAD is an online 3D modeling and slicing software.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
PathEngine - PathEngine is a middleware toolkit for the implementation of intelligent agent movement, built around and implementation of points-of-visibility pathfinding on 3D ground surfaces.
Wings 3D - Wings 3D is a subdivision modeler inspired by Nendo and Mirai from Izware.
Clara.io - Free online 3D modeling software: Design, editor, animation, rendering, & lots of free 3D models. Supports Three.JS, Blend, FBX, OBJ, V-Ray, Babylon.JS, STL.
ZBrush - ZBrush is a digital sculpting and painting software solution.