Kart Kingdom is an MMO that was released in March 2015. The blog is posted by K, and the first blog post was 'Welcome!' which currently has 2,000+ comments. In Kart Kingdom, you will first be asked to choose your avatar's gender. Next, you will be required to customize your avatar and choose a kart. Then, you start a tutorial. When you complete it, you will have to create an account, and then you will be able to play with all of your friends in the Kingdom.
Many great users that play it are found on the Kart Kingdom PBS kids wiki, and the Kart Kingdom wiki.