Google released a new Sidewiki "sidebar" web element. Google Sidewiki allows visitors to your website to contribute helpful information and read other visitors' insights alongside the pages of a website. "Sidebar is a Sidewiki button, which, when clicked, displays a fully functional Sidewiki sidebar to left of the page content. This means that your visitors can see Sidewiki content for your page even if they don't have Google Toolbar or Sidewiki Chrome extension installed," explains Google.
You can choose from exisiting look and feels or create your own. Using the wizard, choose desired look and behavior, then embed generated code in your page.
More Info: Google Sidewiki