Authorstream- Free web-based service that allows uploading and sharing of presentation slides and audio. Includes PresentLive feature that lets viewers follow and chat about your live presentations on their own computer.
SlideServe - Upload and share PowerPoint presentations publicly or privately.
Slideshare- Free web-based service that allows uploading and sharing of presentation slides and audio. Includes tool to sync audio with individual slides. Has also social features allowing users to follow and comment on favorite presenters, topics, etc.
Voice Thread is a collaborative, multimedia slide show that holds images, documents, and videos and allows people to navigate slides and leave comments in 5 ways - using voice (with a mic or telephone), text, audio file, or video (via a webcam).
** A subscription is required for Voice Thread. An individual subscription is $99/year.
For more information on how to use Voice Thread, please click HERE
(Video embedded below is from RadfordEducation)