It is often said that anarchism is entirely impractical. An enumeration of anarchist experiments and moments in history does not entirely refute this claim. But it may be of interest nevertheless. If y'all have suggested additions, I'd love to hear them.
tribal societies: what is and what is not a political state is obviously a hard question, but many tribal societies surely have none. One thing we might point out: people have been around for hundreds of thousands of years, the political state for perhaps 4,000. Call this the period of civilization if you like, or of terminal illness. Michael Taussig has argued that the tribal peoples of pre-columbian Americas were perfectly aware of the state alternatives (as, the Inca empire), and took active measures to reject it.
Peasants' War: The radical reformation, with leaders such as Thomas Muntzer, attacked all established Church and political authorities and "liberated" the town of Allstedt. He was, well, beheaded, but many radical reform sects, such as Anabaptists, set up independent communities throughout northern Europe in the decades that followed.
Diggers: The most radical faction of the English revolution in the mid-seventeenth century, they set up small independent agrarian communities on the common in Cobham, Surrey. Gerrard Winstanley.
American Utopias: Because the American frontier was rather unsupervised, many radical protestant sects set up shop to escape the political authorities in Europe, from the 17th through the 19th centuries. These were followed by many secular experiments that essentially declared their independence from the state. many such communities were relatively enduring and successful. One might mention: Rappites, Shakers, Modern Times, Brook Farm, Oneida, Hopedale.
Revolutionary Ukraine: Anarchists were of course one element in Russia during the revolutionary period. Nestor Makhno organized the Ukraine along anarchist lines from 1919-1921, and successfully resisted the Bolsheviks before finally getting crushed.
Spanish Civil War: Anarchism was a major element in the Spanish Civil War and resistance to fascism in the late 1930's, led by figures such as Buenaventura Durruti. They managed to hold parts of the country for substantial periods of times, organizing them in as free a manner as possible, given the military pressures.