XGAP is a graphical user interface for GAP, it extends the GAP library
with functions dealing with graphic sheets and objects. Using these
functions it also supplies a graphical interface for investigating the
subgroup lattice of a group, giving you easy access to the low index
subgroups, prime quotient and Reidemeister-Schreier algorithms and
many other GAP functions for groups and subgroups.

At the moment the only supported window system is X-Windows X11R5,
however, programs using the XGAP library functions will run on other
platforms as soon as XGAP is available on these.