This is an command-line front-end for the Rakudo Debugger. When you build a current Rakudo Perl 6, you will get perl6-debug binaries that require this (or a compatible) module to be installed.
To use the debugger, just run your script with perl6-debug rather than perl6. It takes the same set of options as the normal perl6 executable, such as -I and -M.
For information on available commands, type h then hit enter for the help screen once you're in the debugger. You may also like to see: