Prior to the time of this post there had already been JSON::PP and Mojo::JSON (which became JSON::Tiny in Oct2012)...
I just want to clarify this: If you skim to the bottom of the POD for JSON::Tiny you will find this:
ACKNOWLEDGEMENTS: ...to Randal Schwartz for showing the Los Angeles Perl Mongers (Sept 2012) his embeddable pure-regexp JSON parser, and explaining it on PerlMonks (995856). He wasn't involved in JSON::Tiny, but it was the exploration of alternatives to his solution that led to this fork of Mojolicious's JSON parser.
JSON::Tiny wouldn't exist if it weren't for two things: First, for the work that Sebastian and his team did to bring us Mojo::JSON as a component of the Mojolicious framework. And second, if merlyn hadn't elevated my interest in the topic by presenting his pure-regexp solution at Los Angeles Perl Mongers in September 2012.
I won't try to put words in his mouth or explain the rationale that he presented at LA-PM for the regexp monstrosity (or thing of beauty). My understanding was that he needed a light-weight JSON parser that he could embed in a $project. He was justifiably proud of the regular expression solution. And while it's certainly fewer lines of code than JSON::Tiny, I believed that there might be a more robust way to embed a pure-Perl JSON parser in a project.
A few days later I found myself thinking about it again, and remembered that one of Mojolicious's philosophies is to minimize external dependencies. That meant that Mojo::JSON should be pretty easy to adapt to a stand-alone module. ...and after working around its use of Mojo::Base and Mojo::Utils, the conversion to a standalone module that could (if absolutely necessary) be copy/pasted right into a code base was straight-forward; JSON::Tiny came into existence.
Mojo::JSON on its own wouldn't have worked for merlyn, because it relies on Mojo::Base and Mojo::Utils. I had to embed the functionality that Mojo::JSON needed from those two modules before JSON::Tiny could be made stand-alone. The test suite also required a bit of adaptation. The tests were almost all identical to their Mojo::JSON versions, but in JSON::Tiny the test suite had to emulate some of the support functionality that the Mojolicious framework would have provided.