You haven’t specifically mentioned what’s your use case or if you actually need a hexahedral mesh.
Hexahedral meshes are awesome because when they’re properly built they provide such a regular shape and means of connecting adjacent cells. It would seem plausible to use a twisted box method to fill a volume with a repeating pattern. Though making a nice hexa mesh from a generic volume is quite difficult…
However, as @Michael_Pryor had mentioned, tetrahedral “triangular” 3D meshing is much easier. Have a look at this old thread: https://www.grasshopper3d.com/forum/topics/shortest-walk-tapered-branching-script?commentId=2985220%3AComment%3A1463585 where Nik implemented Tetgen into Grasshopper to great effect.
Here’s something I was able to get quite quickly out of that Tetgen interface:
Just from intuition, if you’re looking at creating a very stiff and material efficient structure, tetrahedral is probably better than hexahedral. The hexahedral structures look really vulnerable in their shear plane and probably behave in a very anisotropic fashion where as a large enough tetrahedral mesh might be fairly isotropic (? just a guess here).
Have a look at FEA/FEM tools such as OpenFoam, Salome Meca, Code-Aster for some existing volumetric meshing tools.