Markup is a tool that allows a teacher to write and mark a website which can then be shared. This is a great way to share and highlight ideas and draw students' attention to specific ideas.
There are plenty of tools out there that allow a teacher to highlight specific areas of a page, but this one allows you to write with a marker, use circles, use rectangles, insert arrows, and insert text in a variety of sizes and colors. It is really easy to use and intuitive.
Markup provides a bookmarklet that you click when you are on a page that you want to mark. You can mark whatever you want, and then you can publish your marks. You will receive a URL to share with your students (or with whomever you want to share your marks).
Here is my example from a page on the History Channel website: http://markup.io/v/a3yy2taj7kbd
And here is a screenshot:
I circled a video and used the text and arrow tools to highlight areas of the text.
What makes Markup stand out? Others can reply and add their own marks, so you can ask students to find specific items, and they can respond when they do. The conversation can go back and forth. There are many uses for such an interactive engagement with a site - groups of students can work together to mark up important areas of a site when researching.