It’s a bit of a challenge to describe Spreecast in a nutshell — hence the clumsy headline.
Watching the service is sort of like eavesdropping on a videochat between a small group of people; only you can also interact with other viewers, and the videochatters (I hereby coin this word) themselves, through live (text) comments. Spreecast has been used by a bunch of big organizations and famous people — a few standout examples include Reese Witherspoon, The Wall Street Journal, VH1 — to broadcast conversations and interviews. Of course, peons like me (or you) can also use Spreecast to broadcast our own chatter.
Spreecast is old news, since it’s been around since late 2011; but now it’s available as an iPhone app.