Short answers, pulled from the story.
Henri de Saint-Simon, Charles Fourier, Étienne Cabet, and Robert Owen defined early socialist thought. These men shared a belief that people of all classes could voluntarily adopt their plan for society if presented convincingly.
Karl Marx and Friedrich Engels published The Communist Manifesto in 1848. They argued that utopian socialists failed to understand the class struggle between the proletariat and the bourgeoisie.
New Harmony opened its doors in Indiana in 1814 as a community founded by Robert Owen. Brook Farm began operations in Massachusetts during 1841 under Charles Fourier's influence while North American Phalanx started in New Jersey in 1843 with Fourierist principles.
Edward Bellamy published Looking Backward in 1888 as a utopian romance novel about a future socialist society. In Bellamy's vision property was held in common and money replaced with equal credit systems.
Most of these communities failed within a few years due to internal conflicts or financial difficulties. Karl Marx claimed these small experiments were necessarily doomed to failure because they appealed to society at large without distinction of class.