VoiceThreads is an online collaboration where there is an instructional video and students can leave feedback through typing, audio or video. The students don't really interact with each other and it is just passive learning if the instructor isn't constantly checking back on it. So it really is just like thread conversations.
However, I do enjoy it because not only does it have the option for the instructor to add videos, audio and slides, but it also allows to link information from Khan Academy or New York Public Library. Not only can you put a slide up, but you can record yourself speaking about it at the same time and it will appear to the left of it.
A downside is that it is very pricey. Prices depend on grade level you are teaching and whether single instructor or institution.
For all of you online course designers, you can get a VoiceThreads certification for a 2 week online course plus capstone project prices at $199. I saw one of the UAF eLearning professors on it. So I thought to mention it.