The app allows users to broadcast live video from their smartphone cameras to anyone on the internet, either publicly or privately to a selected list of people.
"We’ve always imagined Periscope as a visual pulse of what’s happening right now," wrote Periscope in a post on Medium today.
Work on Periscope began a year ago and the developers of the app have been working with Twitter since January.
The app already has enthusiastic supporters. Former Canadian astronaut Chris Hadfield mused about how the app would be used in a live stream Thursday morning.
The ability to stream video privately has been noted as an especially attractive feature — one that's missing from Meerkat.
However, it is Periscope's first day and the content on the app leaves much to be desired.
The app launched on the iPhone App Store today with an Android version coming soon.