Hi Vanessa,

I'm a developer of SMILI and it has a GUI application for viewing VTK files, overlaying them with images, processing geometry and extracting scalars etc. as a stand-alone application. You can just use drag-n-drop and right click mechanisms for these actions and installers are provided for Windows, Mac OSX and Linux. Check out the NTIRC page or the YouTube channel for tutorial videos/examples.

Cheers
Shakes