Socialism was a political and economic philosophy practiced on Earth worldwide as of the 22nd century.
In 2259, Pelia recalled remaining in her bunker in Vermont, just in case the New World Economy (or, as she put it, the "no money, socialist utopia thing") didn't last. (SNW: "Tomorrow and Tomorrow and Tomorrow")
On the 24th Century in the Bajoran space station Deep Space 9 the Ferengi Rom start reading the writings of Karl Marx, a Human socialist philosopher, including the Communist Manifesto. This inspired Rom to form a workers' union and other actions that were considered taboo at the time by the Ferengi society. (Deep Space 9: (DS9: "Bar Association") Rom would eventually became Grand Nagus of the Ferengi Alliance and, although he remained a capitalist (LD: "Parth Ferengi's Heart Place") he continued his predecessor's social reforms which, although moderate for Marxist standards, were very radical for Ferengi standards. (citation needed • edit)