Online language lab. Allows you to create speaking, listening, reading, and writing assignments that students do online. You can provide feedback to them through the interface.
Google's social network. The "hangout" feature lets you do videochat, including some virtual classroom tools.
Limitations: Hangouts are limited to 10 participants.
backchan.nl is tool for involving audiences in presentations by letting them suggest questions and vote on each other's questions. backchan.nl is intended for conference or event organizers who want a new way to solicit questions from the audience and make better use of question and answer time.
TodaysMeet helps you embrace the backchannel and connect with your audience in realtime.
Encourage the room to use the live stream to make comments, ask questions, and use that feedback to tailor your presentation, sharpen your points, and address audience needs.
Text Message (SMS), Twitter, and web Polls and Voting, Audience Response System
Now includes presenter tools so that you can create polls on the fly (during a presentation).
Can embed live poll results in a PowerPoint or Keynote presentation.
Limitations: Free version allows up to 40 responses.