GSA Auctions (Official Site) is a modernized version of the open auction that sells a variety of different property types (over 51+ categories!) to the general public. Officially stated, "GSA Auctions is the federal government’s online clearinghouse for surplus federally owned assets, ensuring maximum value for customer agencies and American taxpayers". There are 3 basic reasons why property ends up for auction on the GSA portal:
The property was seized by law enforcement
The property was seized by tax authorities (IRS) for failure to pay income taxes or violation of other tax law
The government agency is no longer in need of the property.
Although there are many online government auction sites, the GSA only sells property for the federal government. States may have their own property disposal process and operate online auctions elsewhere. Auctionwiser has no affiliation with the GSA entity.