From Tiny Pictures:
The leading service for real-time sharing of cameraphone pictures and videos between friends. Radar can be accessed from PC browsers, mobile phone browsers, and through a series of applications for mobile devices including the iPhone.
Radar for iPhone offers the full range of picture sharing and conversation features available on all Radar platforms, and adds a clean, highly interactive user experience specially tuned for the iPhones touch interface. Additionally, Radar for iPhone supports streaming of video clips shared on Radar.