I think Forth is particularly notable for providing metaprogramming facilities which are arguably on par with Lisp while taking a completely different approach.

I think Forth is particularly notable for providing metaprogramming facilities which are arguably on par with Lisp while taking a completely different approach. Lisp represents code and data the same way and can manipulate both with ease. Forth has what might be described as an "interactive compiler" which can be easily extended during the compilation process. Since an immediate word can hijack the parser, you could theoretically build Forth out into a reasonable facsimilie of any other language if you so desired. These capabilities are already used in most Forth distributions to provide things like flow control, comments and string literals.