This is Now is a new web project that uses the Instagram API.

It currently offer support for five cities around the world. You get to see photos shared by Instagram users in these cities in real-time.

The five cities are:

New York, United States
Sao Paulo, Brazil
London, United Kingdom
Tokyo, Japan
Sydney, Australia

The developers spoke about the project:

This is Now project is a visual composition which uses real-time updates from the ever popular Instagram application based on users geo-tag locations. The tool streams photos instantly as soon as they are uploaded on Instagram and captures a cities movement, in a fluid story.

Update: The service appears to be overloaded at the moment.