Periscope by Twitter
It's weird how these app fads go. I used to work for a company in Charleston, SC that has been doing live streaming for almost a year now (<a href="http://stre.am/" rel="nofollow">http://stre.am/</a>). They got some press out of SXSW, but without a voice in the Si Valley echo chamber, I suspect they're going to get crowded out.