This virtual classroom/web meeting application allows you to meet with up to 200 people for free. You can video chat, share your screen, run polls, and present PowerPoint shows.
Online Meeting Channels, Audio Conferencing, Screen Sharing, File Sharing, Webinar and Telepresence Solutions
Limitations: 500 free meeting minutes. Up to 4 people in room.
Google's social network. The "hangout" feature lets you do videochat, including some virtual classroom tools.
Limitations: Hangouts are limited to 10 participants.
Create collaborate workspaces that include a wiki-like shared note space, screen sharing, and video chat.
Limitations: 10 people can video chat at the same time. Another 20 people can participate in the conference without video.
Virtual classroom with whiteboard, text chat, audio chat. You can upload images to the whiteboard, draw, and enter text. No registration required. Words on iPads as well as web browsers.
Limitations: No video chat. No option to upload a PPT or PDF.