A low-poly 3D model editor.
Make Human
MakeHuman is used as a basis for a lot of characters used in art of different styles and methods, like creation of comics and cartoons,animations, full scenes in Blender and other software or using only parts of the human body combined with technical or artificial elements.
Gmsh
A three-dimensional finite element mesh generator with built-in pre- and post-processing facilities.
SOLVESPACE
SOLVESPACE is a free (GPLv3) parametric 3d CAD tool.
Goxel
You can use goxel to create voxel graphics (3D images formed of cubes).
F3D
F3D is a VTK-based 3D viewer following the KISS principle, so it is minimalist, efficient, has no GUI, has simple interaction mechanisms and is fully controllable using arguments in the command line.
Sweet Home 3D
Sweet Home 3D is a free interior design application
OpenSCAD
The Programmers Solid 3D CAD Modeller
LeoCad
Design virtual models you can build with LEGO® bricks
Dust3D
Dust3D is a cross-platform open-source 3D modeling software.