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).
enGrid is an open-source mesh generation software with CFD applications in mind. enGrid uses an in-house development for surface meshing and prismatic boundary layers; a module for hex far-fields will be added in the next release.
ANSA is an advanced multidisciplinary CAE pre-processing tool that provides all the necessary functionality for full-model build up, from CAD data to ready-to-run solver input file, in a single integrated environment.