What is the title of JK Rowling book being released in December 2008?

The JK Rowling book released in December 2008 was "The Tales of Beedle the Bard".

This was a collection of children's stories mentioned in the Harry Potter series, which Rowling wrote and illustrated herself. It was released as a charity book, with all proceeds going to Lumos, a children's charity founded by Rowling.