  FermiSurfer is a newly developed Fermi-surface viewer designed to facilitate
the understanding of the physical properties of metals. It can display the
Fermi surfaces of a material, color plots of arbitrary $k$-dependent
quantities, the Fermi surface at arbitrary cross sections (Fermi lines), cross-
or parallel- eye three-dimensional stereogram views, nodal lines, extremal
orbits, and highlight the occupied or empty side of the Fermi surface. In
addition, various first-principles software packages can produce input for
FermiSurfer. This paper explains how to use FermiSurfer and demonstrates its
usefulness by investigating the origin of the anisotropic superconductivity of
YNi$_2$B$_2$C.
