CMC - Mailchimp for Joomla! integrates with the Mailchimp API and shows you your lists and users directly in your backend. In addition to that you can subscribe new users to your lists directly from your backend, or you can use the module to display a newsletter subscription form for them in the frontend.
CNotes - let your user create private notes on your pages!
CNotes was developed as part of the "Joomla extension development masterclass" in July 2012. Together with our students we've explored the Joomla framework and have build something that is hopefully useful to you as well! If you want to learn how to build Joomla extensions on your own, maybe you should visit dothewebinar.com and book the next free webinar!