GRAPE is a GAP package for computing with graphs and groups, and is primarily designed for constructing and analysing graphs related to groups, finite geometries, and designs.
The vast majority of GRAPE functions are written entirely in the GAP language, except for the automorphism group and isomorphism testing functions, which by default use Brendan McKay's nauty package.
L.H. Soicher, Computing with graphs and groups, in Topics in Algebraic Graph Theory (L.W. Beineke and R.J. Wilson, eds), Cambridge University Press, 2004, pp. 250-266. PDF preprint.