Wikispaces qualifies. I've been using Wikispaces for various purposes and recommending it to others since I started this blog. Over the years I've created screencast videos about how to use it, created slideshows about how to use it, and linked to other educators' tutorials on it. But until very recently, Wikispaces didn't have its own YouTube Channel dedicated to showing you how to use the features they offer.
The Wikispaces YouTube channel contains 25 screencast videos created by Wikispaces to show you how to utilize some of their useful features. Below I've embedded their introductory video and their video on creating an educational wiki.
Learn more about the new Wikispaces YouTube channel on the Wikispaces Blog.