GComb
GComb is a gCode viewing tool with an interior focus
...It works by parsing GCode files and producing an image for each layer of the printed object, any of which can then be viewed.
GComb was originally written on Mac OS X using Eclipse with Java version 1.7.0_25, and was made for a Makerbot™ The Replicator Dual printing Skeinforge 50-generated GCode files. The jar file in the package was compiled for use by Java versions 1.5 and greator but, its compatibility on different operating systems and utility for different printers and slicers than those it was written for is not assured. However, we coders did our best to make sure that our implementation would not depend on comments in GCode or slicer-specific details, so it should work given files generated by Slic3r and others as well as Skeinforge.