rep is a lisp created by John Harper? that combines features of emacs-lisp, common lisp and scheme, and arose from a refctoring of the jade emacs-alike that was first implemented by John on the Amiga many years ago: what was then jade-lisp became rep and was reused in other ptojects. See scheme-vs-rep for a comparison of the language to scheme.
rep drives the sawfish (gtk+-based) window manager, as well as being used for scripting jade and web serving via the mod_rep Apache module.