The Fate series began as a lengthy visual novel that has three major storyline branches which serve and a starting point for the many games, anime, and other media within the franchise. The visual novel has adult themes and nudity but would be released in 2007 without nudity.
Typically the series follows the Holy Grail War, a competition where summoners use familiars, usually powerful ancient heroes, to fight for them as they scheme and battle their way to victory. Some offshoots of the series cover different endings from the original visual novel which includes Fate/Zero, Unlimited Blade Works, and others.
Like TYPE-MOON's other franchises, Fate has the theme of magic and fantasy in the modern world. In particular, Fate focuses on mages and legends. It takes place in the same universe as Tsukihime.