What are government databases?

Government databases collect personal information for various reasons (mass surveillance, Schengen Information System in the European Union, social security, statistics, etc.).

Some examples of US databases are:

TALON (Threat and Local Observation Notice): A database maintained by the Air Force after the September 11th terrorist attacks. It was created in 2002 by Deputy Defense Secretary Paul D. Wolfowitz, in order to collect and evaluate information about possible threats to U.S. servicemembers and civilian workers in the US and at overseas military installations. The database included lists of anti-war groups and people who have attend anti-war rallies.

ECHELON: this name is used in global media and in popular culture to describe a signals intelligence collection and analysis network operated on behalf of the five signatory states to the UKUSA agreement; Australia, Canada, New Zealand, the United Kingdom and the United States.

Guardian: The Guardian Threat Tracking System is a reporting system used by the FBI to track threats and other intelligence information. It was established to collect data on terrorist threats and suspicious incidents, at seaports and other locations, and to manage action on various threats and incidents.On August 21, 2007, the US Department of Defense announced that Guardian would take over data collection and reporting which was previously handled by the Talon database system.

Sources:
http://en.wikipedia.org/wiki/Government_database
http://en.wikipedia.org/wiki/TALON_(database)
http://en.wikipedia.org/wiki/ECHELON
http://en.wikipedia.org/wiki/Guardian_(database)
http://www.defense.gov/news/newsarticle.aspx?id=47127