I know a guy who once completely replaced the init system on his Linux box with a custom system written in Perl.

I made serious headway into recreating the complete set of standard unix core utilities (excepting C compiler, et alii) in Perl, but ultimately gave that up as a goal because I discovered I actually want to complete that task in OCaml -- including, eventually, an OCaml compiler. First, I've got to learn more Ocaml, though. I'm not even at a level of mediocre competence in that language yet.

I'm currently looking at the possibility of using Perl to write interpreters for other languages -- such as Logo -- in Perl such that I can upload the interpreter to the cgi-bin of shared hosting accounts. This, of course, would be for the purpose of using some rather edge-case languages for web development, mostly for the perverse joy of it.

Maybe someday I'll use Perl to write a binary compiler for Perl. I sincerely doubt it, though.