TetGen is described as 'program to generate tetrahedral meshes of any 3D polyhedral domains. TetGen generates exact constrained Delaunay tetrahedralizations, boundary conforming Delaunay meshes, and Voronoi partitions'. There are more than 10 alternatives to TetGen for a variety of platforms, including Windows, Linux, Mac, Android and iPhone. The best alternative is Blender, which is both free and Open Source. Other great apps like TetGen are Wings 3D (Free, Open Source), SALOME (Free, Open Source), Gmsh (Free, Open Source) and MagicaCSG (Free).
Wings 3D is a subdivision modeler inspired by Nendo and Mirai from Izware. It is possible to assign materials, vertex color, UV coordinates and textures, but there will be improvements in those features before Wings goes 1.0.
Gmsh is a 3D finite element grid generator with a build-in CAD engine and post-processor. Its design goal is to provide a fast, light and user-friendly meshing tool with parametric input and advanced visualization capabilities.
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.
picoCAD is a program to build and texture lowpoly 3D models. Programs for modelling are overly complicated, picoCAD aims to make it fun, easy, and accessible by focusing on the bare essentials. This program was made using pico 8.
HyperMesh is a market-leading, multi-disciplinary finite element pre-processor which manages the generation of the largest, most complex models, starting with the import of a CAD geometry to exporting ready-to-run solver file.