Software Manuals:

SM (graphing program, in postscript)

FITSIO Library (FITSIO Home Page)

CFITSIO (C version, in postscript)
FITSIO (Fortran version, in postscript)
The Original FITS Definition.

HEALPIX Software manuals  (The HEALPIX Home Page)

Introduction to HEALPIX (AKA The Healpix Primer)
HEALPIX Programs (AKA Fortran Facility User Guidelines)
IDL Procedures (AKA IDL Facilities Overview)
Fortran Subroutines (AKA Fortran90 Subroutines Overview)

CMBFAST (The CMBFAST Home Page)
IDL Astronomy User's Library (HTML)