.hack//G.U. is the title of a series of three video games for PlayStation 2. The first title in the series, Vol.1 Rebirth, was released on Japan on May 18, 2006 and on October 24, 2006 in North America. Vol.2 Reminisce was released on September 28, 2006 in Japan and on May 8, 2007 in North America. Vol.3 Redemption was released on January 18, 2007 in Japan and on September 10, 2007 in North America. .hack//G.U Trilogy the movie, was released on DVD and Blu-ray on March 25, 2008 in Japan.

The games take place after the .hack//Roots anime series. .hack//Roots serves as a prologue to the G.U. video game series in the same way the .hack//Sign anime series served as a prologue to the four original .hack//Games.

Source: Wikipedia