The Wikipedia article for "webcast" states that "webcasting usually refers to non-interactive linear streams or events" and that "essentially, webcasting is broadcasting over the internet." There is absolutely no reason for webcasts to be "non-interactive." You're doing yourself and your audience a disservice if this is the case. At the University of Pennsylvania, we've done dozens of interactive webcasts, trying many new tools along the way.
Notebook / Blog
Rather than a blog, I like to think of this space as a personal notebook that is open and available for all to see. If I'm already keeping notes for my own various uses, why not share them publicly and hopefully provide value to others as well?
With Google Hangouts On Air, you can host and broadcast live discussions and performances to the world. You can also embed the live video player into a webpage with an html code, and later edit and share a copy of the broadcast. At the University of Pennsylvania, I've done dozens of complex, large-scale live webcasts using Google Hangouts on Air. Here, I share my findings.