The following documentation is included on the doxygen landing page C++ API documentation

Program description:

The Mantid project provides tools to support the processing of materials-science data. This data can be gathered from Neutron scattering or Muon spectroscopy experiments or as the result of simulation.

Mantid is:

open source
64-bit, cross platform: Linux, Windows, macOS
built using many other open source projects.

The Mantid web page can be found at
https://www.mantidproject.org