K-6
Farmville is not a traditional classroom activity, but there are characteristics from many content areas. Agriculture, Math, ELA, Literacy, economics, social studies, etc... Students can become one another's neighbors and help to build a community in which they care for one another's farms. A downfall to this application is that it is blocked by my district and I would suspect it would be blocked by many. If you choose to request permission from you tech department, please note that this is a web 2.0 tool.
3-12
Teachers and students can collarborate over a public live document. You can invite others to be apart of this experience and its all FREE, no limits.
Cons: No limits, must monitor students.