Ripplon Software Inc.

Free
BiotSavart calculates the magnetic field resulting from general 3-D configurations of current-carrying conductors.
Free
Mac OS program for professional lens design, featuring diagnostic plots, surface shapes, and AGF file import.
Free
Open solid models in such formats as StL, DXF GTS, NFF, etc.
Free
Mac app for viewing and translating StereoLithography files.