Kelp is a very nice web framework if you want to get the most out of Plack. I had a pleasure of heavily hacking on it and developing many improvements, including version 2.00.
I think Kelp still has advantages over other frameworks in two areas: configuration and extensibility. It's extremely easy to change what Kelp does (even easier after I refactored the core), and its powerful configuration model makes it easy and fun to modify and merge configuration fields. In addition, as benchmarks showed, it's probably the fastest non-trivial Perl framework available.
As a result of my activity, in addition to improving the framework itself and putting together improvements which became a new major version, these modules were created (in order of usefulness):