http://vyew.com is a free synchronous collaboration. Once you registered, you can get access to a personal space where you can manage appointments. Except for the Flash plugin, there is no technical installation required. The platform allows to benefit from various solutions like elearning. No video but the main functionalities for a virtual classroom are there:

• blank board – the usual electronic paperboard
• slideshows – automatic PDF conversion, Powerpoint, Word, Excel, Flash animation
• screen share for slideshows viewing, work on the blank board and even more sharing of your desktop to handle a software
• instant messenger – public or private chat
• free call conference

Slideshows are often the main tool in a training course, that is in all training sessions you are likely to encounter the same suite. http://vyew.com makes it possible to save slideshows to reuse them.

The free service is limited to 20 participants whereas the subscription service (for less than 20$ a month) can host up to 300 people.

Certainly VoIP and video streaming functionalities would have been great, in the same time their lack avoids further technical constraints necessary for the service! Although the quality of the screen share may result low (as to rapidity and image resolution), it should be enough to meet most of your needs.