Plack is a reference implementation of the burgeoning PSGI initiative. What is PSGI? Well, if you follow that link you’ll get a more complete explanation, but the short form is that it is a Perl alternative to Python’s WSGI (Web Server Gateway Interface) and Ruby’s Rack. The longer-form is that it’s a specification layer to decouple web applications from the specifics of how they’re being run, whether that’s CGI, FastCGI, Apache with mod_perl, etc. The longer explanation can be had at the link.
Back to Plack: Plack is the first reference implementation of the PSGI spec, and already it can pass all of the Catalyst tests. And as of this commit, the plackup script can coerce a an app written for Catalyst, CGI, etc. into running under different environments, thanks to the magic of PSGI.
I’ll be watching Plack very closely. I see a PSGI connector for my XML-RPC server in the not-too-distant future.