A twitter-like feed that sends text messages to cell phones that let first responders like police and ambulance folks recruit helpful bystanders to assist in managing emergencies.

For instance - I need an entrance ramp blocked so no more cars get on this highway - is there someone nearby who can park their car to block it and wave people around?

Or - how many people are stranded on the other side of this flooded road - can someone nearby give me an estimate?

There should be some well-known way to subscribe to the feed, and it should be able to recognize your physical location.