Draw on any webpage

To date, I've been using Skitch (which is great). Here's another app called MarkUp.
Capture your thoughts quickly and easily by drawing on any webpage. Share your ideas with coworkers, colleagues, and friends. MarkUp works in your browser, so there’s nothing to download and install; just drag the Get MarkUp icon into your bookmarks bar. When you want to make notes on a webpage, click your bookmarklet to load the MarkUp toolbar. Publish when you’re ready to share your thoughts.