Software
The following links provide information about computer programs used for the analysis of neutron reflectivity data. In some case copies of the software are made available to other users. Consult the pages for further details.
(original list from http://www.reflectometry.net, courtesy of Adrian Rennie)
Software with developers engaged with ORSO

A catalogue of neutron reflectivity fitting programs written by Adrian Rennie that also use the Fitfun data fitting package developed at the ILL by Dr Ron Ghosh and the Clickfit GUI
http://www.reflectometry.net/refprog.htm 
Neutron Reflection Analysis DRYDOC and LPROF by Adrian Rennie
http://www.reflectometry.net/fitprogs/drydoc.htm 
Programs for Xray reflectometry analysis by Adrian Rennie
http://www.reflectometry.net/xrefprogs.htm 
Neutron reflectometry programs available from the NIST Center for Neutron Research.
https://www.nist.gov/ncnr/datareductionanalysis/reflectometrysoftware 
Interactive, WebBased Calculator of Neutron and Xray Reflectivity, provided by Brian Maranville at NIST Center for Neutron Research.
https://www.ncnr.nist.gov/instruments/magik/calculators/reflectivitycalculator.html.
There is also an extended version for magnetic samples and polarised neutrons:
https://www.ncnr.nist.gov/instruments/magik/calculators/magneticreflectivitycalculator.html. 
RASCAL  for analysis of multicontrast neutron reflectometry data A. Hughes, RAL
https://github.com/arwelHughes/RasCAL_2019 
BornAgain is a program to simulate and fit grazing incidence smallangle scattering
http://bornagainproject.org 
MOTOFIT: A package that uses IGOR Pro for corefinement of neutron and Xray reflectivity data written by Andrew Nelson, Bragg Institute, ANSTO.
http://motofit.sourceforge.net/wiki/index.php/Main_Page 
refnx: Neutron and Xray reflectometry analysis in Python by Andrew Nelson and Stuart Prescott ANSTO.
https://www.github.com/refnx/refnx 
GenX  a program that uses a genetic algorithm to refine model fits to reflectivity data writen by Matts Björck, Uppsala University.
https://aglavic.github.io/genx/index.html
Other Reflectometry fitting Software

Analyzer is an analysis tool from the ChemMatCARS beamline at APS. Data fitting software for the following liquid surface scattering techniques: Xray reflectivity (XR), grazing incidence Xray diffraction (GIXD), Xray fluorescence near total reflection (XFNTR), and grazing incidence Xray offspecular scattering (GIXOS). https://chemmatcars.uchicago.edu/facilities/software/

AFIT written by Paul Thirtle (3.1) is available from Oxford.
http://physchem.ox.ac.uk/~rkt/afit.html 
Calculate neutron reflectivity on the Web. Alan Munter has provided a WWW site at the NIST Center for Neutron Research. (NOTE: requires Java applet, no longer functional in modern browsers. Source code still available here) https://www.ncnr.nist.gov/resources/reflcalc.html

Description of Norm Berk’s Programs and Papers
https://ncnr.nist.gov/staff/nfb/nxnsr.html 
Description of data reduction for CRISP at ISIS
CRISP data analysis 
SURFace  A Package for Analysis of Reflectivity Data J. R. P. Webster and S. Langridge, RAL
https://www.isis.stfc.ac.uk/Pages/Surfdataanalysis.aspx 
POLLY  for simulation and analysis of polarised neutron reflectometry data S. Langridge, RAL
https://www.isis.stfc.ac.uk/Pages/Crispsoftware.aspx 
MultiFit, SuperFit and other Software for XRay Reflectivity and Polarised Neutron Reflectivity, K. Ritley & W. Donner, MPI f. Metallforschung, Stuttgart, Germany
http://www.is.mpg.de/8137185/fitting. Note: this site and software is no longer avaiable  an archive link is provided for information. 
Reflec95 (for W95/NT) and ReflecMCA (Mathematica) programs for simulation of reflection from magnetic layers available at the LLB, Saclay, France.
http://wwwllb.cea.fr/prism/programs/programs.html This link also provides links to other software by Frederick Ott for offspecular scattering. 
Description of Parrat32 for multilayer reflectivity calculation and fits. This was available from BENSC, Germany but is currently not supported or available for download. Historic documentation is found at www.archiv.org .
Parrat32 
IMD  an IDL package by David L Windt for optical reflectivity calculations
http://www.rxollc.com/idl/ 
A program for analyzing Grazing Incidence Small Angle Xray Scattering on nanostructures by R. Lazzi, F. Leroy, C. RevenantBrizard and G. Renaud, Grenoble.
http://www.insp.jussieu.fr/oxydes/IsGISAXS/isgisaxs.htm 
RFIT2000: a program written in Delphi by Oleg Konovalov at the ESRF, Grenoble to Xray and neutron reflectivity data.
http://www.esrf.eu/computing/scientific/RFit2000/rfit2000.htm 
yanera: fits multiple contrasts using a variety of different minimisation algorithms. Written by Thad Harroun, Brock University.
http://www.physics.brocku.ca/~tharroun/yanera/index.html 
StochFit: StochFit utilizes stochastic fitting methods to model specular xray reflectivity or neutron reflectivity data. Written by S. M. Danauskas et al, University of Chicago. http://stochfit.sourceforge.net/

DANSE  Reflectometry. As part of larger project on software development the University of Maryland provides libraries and applications for reduction, analysis, modeling and simulation of reflectometry data. https://refl1d.readthedocs.io/en/latest/#

FitSuite  a program for fitting reflectometry and other data (such as Mossbauer resonant reflection data) from KFKI, Hungary. http://www.fs.kfki.hu/

Irena  modules for Igor Pro used primarily for smallangle scattering but also for reflectivity. The package is developed by Jan Ilavsky at APS with reflection calculations based on modules from Andrew Nelson (ANSTO). https://usaxs.xray.aps.anl.gov/software/irena

SANGRA: Script Automated Neutron Grazing Reflectivity Analysis package from the Soft Matter and Biophysics group at the University of Santiago de Compostela http://alanine.usc.es/sangra/sangra.php.

AuroreNR: Matlab software developed for the analysis of neutron reflectivity data by Yuri Gerelli at the ILL, Grenoble. http://sourceforge.net/projects/aurorenr/.

Överlåtaren: program to transform grazing incidence data in to maps in reciprocal space created by Franz Adlmann, Uppsala. http://www.physics.uu.se/research/materialsphysics+/research/oever.

REFLEX: Matlab software developed by Guillaume Vignaud and Alain Gibaud for Xray, soft Xray (incorporating polarisation) and neutron reflectivity fitting. http://reflex.irdl.fr/Reflex/reflex.html.

Multifitting: this is software developped by Mikhail Svechnikov, Moscow for fitting multiple layer structures http://xrayoptics.org/products/softwaremultifitting/

Zeeman Splitting: a Jupyter notebook from Michael Fitzsimmons that accounts for Zeeman splitting in polarized neutron reflectometry data https://github.com/mfitzsimmons44/reflectometryanalysis

anaklasis: a set of opensource Python3 scripts (with fortran90 extensions) that facilitate a range of specular neutron and xray reflectivity calculations https://github.com/alexandroskoutsioumpas/anaklasis

ESCAPE: Python/C++ package with full integration to Jupyter project. Provides solutions for different scattering problems, like reflectivity, small angle scattering, high resolution xray diffraction, gammaemissions, etc. Overview: https://arxiv.org/abs/2011.01340 https://escapeapp.net