Markup.io offers a variety tool to help you draw and write on any web page without downloading any software.
You can launch Markup on any page by clicking the bookmarklet or using their Chrome browser extension. When the toolbar loads, you will have to option to write text notes or create freehand drawings on the current page in various colors. When you are done, hit the Publish button and share it with friends.
Markup also supports a variety of keyboard shortcuts to ease the process of marking up. For instance the letter ‘t’ will switch to Text mode while ‘c’ will let you draw a circle. You can use the Shift and arrow keys to nudge selected shape /drawing by 10 pixels.
When you share a Markup document with someone, they will can choose the “Reply” option to edit the existing markup or add their own.