> 5
According to https://en.wikipedia.org/wiki/ISLisp , there are a few partial modern implementations and two full ones. OpenLisp ( http://www.eligis.com/ ) is commercial (with support), but you can download an executable for non-commercial use. Easy-ISLisp ( https://github.com/sasagawa888/eisl/ ) is open-source, 2-clause MIT.
Although it's not a subset (which I think was a mistake), I've even played around with running ISLisp programs under sbcl. This involves some trivial substitutions, e.g. do->for, (standard-output)->*standard-output*, etc. There is a macro package to do this automatically ( https://github.com/ruricolist/core-lisp ).
I just like that it "looks" very similar to both ANSI CL & ELisp, while being smaller/easier to learn than CL at least. Kind-of follows the principle of least surprise.