I realize that you are looking for a free service, but I decided to share this anyway.
I have experience with hotComm
(I am participating in some webinars that use this software). The client software is free for people attending the webinar, but I think that the presenter should have the paid version, not too sure about that. Still, the software is not without problems and glitches. And, people need to download and install the client.
Now, the good things about it, you have voice and video, you have drawing tools to add some notes or arrows or simple drawings on top of your presented images/video, people can record sessions (although for full video recording the paid version is necessary).