NRFit
Neutron and x-ray reflectivity analysis in IgorPro environment / nrfit
...First time users might also want to turn ON the ShowTips from Graph menu. Have IgorPro6.0MAC? Follow the NRfit link and browse the All files, and download the nrfit osx 6.0 version.
Downloads:
Download a proper version (window, mac) from the 'Browse all files' menu.