BornAgain is an open-source research software to simulate and fit neutron and x-ray reflectometry, off-specular scattering, and small-angle scattering (SAS), especially under grazing incidence (GISAS).

Its name, BornAgain, alludes to the central role of the distorted-wave Born approximation in the physical description of the scattering process. The software provides a generic framework for modeling multilayer samples with smooth or rough interfaces and with various types of embedded nanoparticles.

BornAgain almost completely reproduces the functionality of the widely used program IsGISAXS (Lazzari 2002, Lazzari 2006). BornAgain goes beyond IsGISAXS by supporting an unrestricted number of layers and particles, diffuse reflection from rough layer interfaces, particles with inner structures, neutron polarization and magnetic scattering. Thanks to a consequential object-oriented design, BornAgain provides a solid base for future extensions in response to specific user needs.

BornAgain is a multi-platform software, with active support for Linux, MacOS and Microsoft Windows. It is free and open source, available under the GNU General Public License (GPL v3 or higher).

For a broad overview, see the journal article J. Appl. Cryst. 53, 262–276 (2020), which is also the primary means to cite BornAgain in scientific publications.