Draw3D is a 3D rendering tool written entirely in VTK-TCL script. It is intended for fast command line rendering and visual inspection of datasets commonly found in medical imaging. It also allows the generation of images for reports or videos. As it is based on pure VTK, it can render whatever VTK can render, and runs wherever VTK can run.
Meshinator is a simpler tool that uses VTKs isosurface functions to generate meshes from volumetric data.
The Apache License is a free software license authored by the Apache Software Foundation (ASF). The Apache License requires preservation of the copyright notice and disclaimer, but it is not a copyleft license — it allows use of the source code for the development of proprietary software as well as free and open source software. (From http://en.wikipedia.org/wiki/Apache_License)