Very cool. It looks like Google packaged a few of their services together (docs, picasa, sites), and developed a few tools specifically for wedding planning. I'm not sure how it compares to the Knot tools, but if you already have a Google account, it might be worth checking out.
http://www.google.com/weddings/ 
Baby #2: Surprise BFP 9.19.12, EDD 5.24.13, natural m/c 10.19.13 at 9w