CAMB (Code for Anisotropies in the Microwave Background, http://camb.info) is a FORTRAN 90 program for computation of the linear stage of evolution of primordial density perturbations and Cosmic microwave background anisotropies as a function of cosmological parameters.
The code was originally written by Antony Lewis and Anthony Challinor.
See also: Cosmic Linear Anisotropy Solving System – a more recent Boltzmann solving code