Which SW for 2.5D work?

For importing an STL the commercial Carbide 3D options are:

MeshCAM:

or Alibre Atom3D Workshop if you also need CAM:

and Carbide Create Pro:

For the specifics on the latter, see:

A free program to replace PathCAM is Carbide Create v6:

There are various free and opensource options, and other commercial ones. What sort of STLs are you working with and how do you intend to approach them?