SHOP and SHOP2 are HTN planning systems that were designed with two
goals in mind: to investigate some research issues in automated
planning, and to provide some simple, practical planning tools.  They
are available as freeware, and have developed an active base of users
in government laboratories, industrial R\&D projects, and academic
settings.  This paper summarizes how SHOP and SHOP2 work, describes
some of the applications that we and others have developed for them,
and discusses directions for future research and enhancements.
UMIACS-TR-2004-46