It doesn't pass my smell test. They don't even say what flavor of Lisp they support (ANSI Common Lisp, Scheme, ...). And a TCL/Tk GUI? How 1998.
For what it's worth, Guile is a Lisp-y glue language too, and it's almost certainly more mature than newLISP. What's more, there's a Perl binding: Inline::Guile.