MediaG3 (MDGC)

[Cassandra]

Hexa2 and Netstairs' platforms do not require downloads.

Actually, that's not true. An Adobe Flash Player is required. https://hexa2.com/requirements

There are security problems with the Adobe Flash Player:
http://www.pcworld.com/article/261371/beware_adobe_flash_is_under_siege_.html

http://www.nbcnews.com/technology/technolog/adobe-flash-player-hit-hackers-both-ends-959551

http://www.pcworld.com/article/262045/adobe_admits_flash_exploits_threaten_windows_8.html

Even Adobe's own webconferencing platform does not require its Flash Player. http://www.adobe.com/products/adobeconnect.html

Many of the popular web conferencing platforms require no download at all.

Read the reviews here: http://www.socialbrite.org/2011/01/19/comparison-top-web-conferencing-services/ None of these require downloads:

http://www.watchitoo.com/

http://www.infiniteconferencing.com/index.php

http://www.gotomeeting.com/fec/webinar

http://www.readytalk.com/

https://www.zoho.com/meeting/

http://www.webex.com/

http://www.microsoft.com/en-us/office365/lync-online.aspx

https://www.yuuguu.com/s/home

https://www.ibm.com/cloud-computing/social/us/en/

http://www.hearme.com/

In addition to their top 15, here are some others referenced in links from their site.

Promising newcomer: https://www.meetingburner.com/

Supports mobile: https://www.fuzebox.com/