The Mesh&More mesh generator
Mesh&More is a dimension-independent mesh generator based on spacetrees (generalised octrees). That is, Mesh&More works on a volume-based geometry representation (such as medical image data), in contrast to most other mesh generators which work on a surface-based geometry.
Mesh&More can generate hexadral semi-structured meshes with fixed spatial resolution, and unstructured tetrahedral or hybrid meshes (containing tets, cubes and pryramids) with spatially varying (non-uniform) resolution.
A volume-oriented representation means that for every point in space an efficient query for properties is possible. The most basic case is whether that point is part of the geometry or not. Slightly more advanced is a query which (sub-)region the point lies in, for instance defined by material type in a segmented medical image. Subregions are problematic for most surface based representations which typically expect a single region bounded by a smooth surface (mathematically speaking, they expect the region surface to be a sufficiently well-behaved manifold). Thus, a volume-oriented geometry description is a more natural choice for meshing volumetric data sets which have no readily available surface-based representation, in particular not one which is smooth and manifold. Representation of internal material boundaries is built into the volumetric representation almost by definition (although this does not mean it is easy to generate good meshes for each configuration of internal boundaries). Furthermore, it is (in principle) straightforward to let local properties of the space guide the mesh generation process (type of elements, resolution, algorithm). Again, this does not mean it is always easy to generate good meshes for each combination.