The best open source alternative to Zmodeler is Blender, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 50 alternatives to Zmodeler and 16 is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to Zmodeler are MakeHuman (Free, Open Source), Wings 3D (Free, Open Source), Bforartists (Free, Open Source) and OGRE (Free, Open Source).
Dead Deer is a 3D modeler, 3D game maker, and a 3D demo maker designed to create games. The scripting language allows you to code interactions in pseudo-C with the animation and synthesizes your rendering with your shaders.
OpenFX is an open-source, free modeling and animation studio, distributed under the GNU General Public License. A powerful feature-set includes a full renderer and raytrace engine, NURBS support, kinematics-based animation, morphing, and an extensive plugin API.