Influential dialect of LISP. Developed initially as the standalone PDP-6 LISP at Project MAC, then moved to ITS and renamed MACLISP somewhere along the way. Later ported to TOPS-10, WAITS, TOPS-20, and Multics.
The MACLISP application Macsyma was so important a consortium was formed to buy a KL10 to run it. When the aging PDP-10 hardware was falling behind, new MACLISP-compatible implementations were written and Macsyma was brought up on those.
Descendants include Lisp Machine Lisp, NIL, Franz Lisp, Common Lisp, and Emacs Lisp.