Blab is a video chat app, which is very similar to Periscope for groups of friends.
Using this app, four people can simultaneously video chat, which an audience can watch, comment, and even instantly switch places with one of the four people.
You will have to log in with your Twitter credentials to participate as a video chatter in one of the 4 squares. Once someone clicks on your name in Blab, they will see your handle and bio as indicated in your Twitter account.
An interesting component of Blab is that it gives you the ability to mute any or all of the four video chatters. So, for example, if three people are interviewing someone, you can choose to mute the three interviewers and just listen to the answers from the interview subject.
The fact remains to be seen if Blab can weather the competition of other video chat apps.