One great example is Amarcord by Federico Fellini. It describes one year in a small Italian town in the 1930s. There is no main character, only a "main family" and a few other related people of various ages with distinct backgrounds. There is no real plot, only a sequence of interesting (absurd, funny, sad) events that happen throughout the year, to varying subsets of those people. The movie is largely fictional, but seems quite realistic, precisely because it doesn't have any main plot to speak of.