Often described as a secure version of Twitter for government, Nixle describes its mission:
Nixle’s mission is to enable government agencies, small to medium size businesses and enterprise-level organizations to communicate in a secure way and exchange multimedia content over a trusted mobile platform. Our product line supports secure enterprise grade communications for both public and private messaging.
(http://www.nixle.com/about.html(link is external))
Read about the West Hollywood Sheriff’s July 2010 adoption of Nixle here.