CMBFAST is a code, written by U. Seljak and M. Zaldarriaga, for calculating the linear cosmic microwave background (CMB) anisotropy spectra based on integration over the sources along the photon past light cone. In this approach the temperature anisotropy is written as a time integral over the product of a geometrical term and a source term.
This software is no longer available for download; you should investigate CAMB in its place.
A collection of journal references describing CMBFAST: