Reference Counting LISP 

Reference-counting Lisp interpreter

from CMU Gloss:
"RefLisp is a small Lisp interpreter. Versions exist for MS-DOS and
UNIX (AIX). The MS-DOS version supports CGA/EGA/VGA graphics and the
Microsoft Mouse. The interpreter is a shallow-binding (i.e.,
everything has dynamic scope), reference counting design making it
suitable for experimenting with real-time and graphic user interface
programming. Common Lisp compatibility macros are provided, and most
of the examples in "Lisp" by Winston & Horn have been run on RefLisp.
RefLisp makes no distinction between symbol-values and
function-values, so a symbol can be either but not both.  RefLisp
comes with an ASCII manual and many demonstration programs, including
an analogue clock which never stops for garbage collection.  There is
also a program profiler."