Techne is a basic modeler .NET program, poorly made well enough that it will not run on Mono (hence it is Windows only). It outputs Java MC-style code that draws a model with no optimizations.
TMT/NMT is a java library, can have it create basic things like cubes and cylinders and such in-code, it can also import obj and blender models for any quality you want, as well as being able to feed it raw polygons and even handle bone animation, it optimizes the calls in to DisplayLists (the best supported by OGL1, which is what MC uses) with a few other things.
Thus, different purposes, which bugs me as to why someone brought up the windows-only-crap Techne. Could just use NMT and make a model in blender or some other real modeling program if you really so wished to use a modeler. I prefer the code method myself.