In short, it was a tool to allow the use of Java and Perl in a single program. It allows you to implement Java methods in Perl code (according to its README).

In fact, it is included in the Perl 5.6.1 and 5.8.0 tarballs under the jpl directory, but it's not installed unless you go into that directory and run the install-jpl script yourself.

Did anyone use it? AFAIK, there has never been any major use of it discussed on any Perl forum. That doesn't mean no one ever used it, but it certainly didn't take off.

Is it dead? I think so. Certainly, no one is maintaining it, and I wouldn't be surprised if it didn't even work with 5.8.0.