PLT Redex consists of a domain-specific language for specifying reduction semantics, plus a suite of tools for working with the semantics.
This is a reference manual for Redex. See http://redex.racket-lang.org/ for a gentler overview. (See also the examples subdirectory in the redex collection.)
Alternatively, use the redex/reduction-semantics and redex/pict modules, which provide only non-GUI functionality (i.e., everything except redex/gui), making them suitable for programs which should not depend on racket/gui/base.