In the BCcampus installation of Moodle we use an annotation tool called Marginalia. It's a fantastic tool for adding your thoughts while reading forum posts. As a facilitator I use it a lot to be quietly active. You may also find it a useful tool for adding short acknowledgements, flagging items you'd like to return to, and just simply being present in a discussion.
This is an example of how I used Marginalia just a few minutes ago. I'm sharing this also so you can learn about the important workaround to avoid error messages.
Branca posted this reply in our Sharing and Feedback forum. Notice when I opened the post the subject has yellow highlighting. IMPORTANT! If you see the yellow, you need to refresh your browser before adding an annotation!
So... I refreshed, then highlighted some text in Branca's post, hit my "enter" key, then typed my annotation. That's it! Very simple, but frustrating if you don't refresh your browser first. There you go, you're ready to add annotations. It looks like this: