What is magical quill in pottermore?

What is "Magical Quill" in Pottermore?

The Magical Quill is located in Hogwarts School of Witchcraft and Wizardry. It detects the birth of a magical child and writes his or her name down in a large book. Every year, Professor McGonagall checks the book and sends owls to the children who are turning eleven, to inform them that they have a place at Hogwarts. The lucky few who locate The Magical Quill during the Magical Quill challenge (which will run from 31 July to 6 August 2011) will have the chance to register for Pottermore early and gain access to the site before it opens to all in October 2011.
Magical Quill