IDNA convert is written and maintained by Matthias Sommerfeld. He is a (freelance) web developer since 2000. Some of his work includes phlyMail. His professional profile (in German) can be found over at XING, his company's website (also in German) is here.
The first version of IDNA Convert came to light in 2004, when IDN domains became available in Germany. The goal was to easily handle IDN domains in various projects. Since PHP does not support IDN domains in the core, it was necessary to code the algorithm in pure PHP.
To get in touch with Matthias, send him an email: matthias [at] sommerfeld [dot] me.
A few people have contributed to the class, namely Markus Nix (Mayflower, Docuverse), Daniel Hahler.
Thank you, guys!