In addition to Perlix (can't find a link) and the Perl shell which are discussed in The Perl Journal #18 (no longer on-line) there is Claudio Calavelli's file system written in Perl.
The thought of this hurts my brain even more than the thought of his INTERCAL compiler written in Perl.
John.
-- And the eighth and final rule, if this is your first time using Perl, you will have to write code.