It’s called WordPress.com Sidebar by GS! Networks.
I just got it right now and I love it. It’s just like Twitkit but for wordpress, and has awesome features like stats and a spellcheck. The disadvantages of this addon are that it’s currently kind of bland, and the spell checker is a separate text field, but that’s circumvented by Firefox’s spell checking capabilities. I would give it 4/5 for anyone who has a wordpress blog.