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.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
SelfCAD - SelfCAD is an online 3D modeling and slicing software.
3D Cityplanner - Urban and real estate development at your fingertips. With the 3D Cityplanner it’s possible to create, visualize, analyze and share 3d plans online.
Silo - Silo is a focused 3D modeling application with the ability to effortlessly switch between organically sculpting high-poly models and precisely controlling hard-edged surfaces.
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.