For a number of years now, I have worked on bringing student literature responses on-line. For the last two years, students have responded to their literature solely on-line. I have tried numerous services trying to find the perfect fit. I began with Mobile Me account (then dot Mac), and then PBWorks (taka PBWiki) our district's podcast server, and a host of others. The biggest problem was that I wanted to have threaded discussions, and there just did not seem to be anything out there. Enter Edmodo.Edmodo has proven to be just what I was asking for (almost). It has a Facebook like feel, with teacher control. You are able to start discussion groups and follow along as students have threaded discussions. They also have an assignments feature that is very nice. You are able to give the students assignments that they fill and the assignment and grade it is kept between the student and yourself. It also includes a calendar, polling option and direct messaging. The best part - it's free. The creator is the husband of a teacher. He saw that his wife was frustrated by the what was available (or not) so he created Edmodo.
Edmodo is always changing. They are constantly updating and adding features. They also have the most responsive and friendliest support I have seen. Simple post a question, and it's answered within a day or less (I usually get replies within a few hours). The same is true about suggestions. If there is something that you would like to see Edmodo do, simply post the suggestion and they will respond. Who knows, your suggestion may be included in the next upgrade.
Check it out at http://www.edmodo.com