The go-to example is definitely Pol Pot's Cambodia. It was basically red fascism but actually real.
Qarmatians: slavery-based socialism
The Qarmatian state had vast fruit and grain estates both on the islands and in Hasa and Qatif. Nasir Khusraw, who visited Hasa in 1051, recounted that these estates were cultivated by some thirty thousand Ethiopian slaves. He mentions that the people of Hasa were exempt from taxes. Those impoverished or in debt could obtain a loan until they put their affairs in order. No interest was taken on loans, and token lead money was used for all local transactions. The Qarmathian state had a powerful and long-lasting legacy. This is evidenced by a coin known as Tawila, minted around 920 by one of the Qarmathian rulers, and which was still in circulation in Hasa early in the twentieth century.