An old and widespread form is the consumers' cooperative, in which people organize for wholesale or retail distribution, usually of agricultural or other staple products. Traditionally, membership is open, and anyone may buy stock. Goods are sold to the public as well as to members, usually at prevailing market prices, and any surplus above expenses is turned back to the members. Money is saved through direct channeling of goods from producer to consumer. Producers' cooperatives are manufacturing and distributive organizations, commonly owned and managed by the workers. Another development in such cooperatives has been the acquisition of failing manufacturing plants by labor unions, who run them on a cooperative basis. Agricultural cooperatives usually involve cooperation in the processing and marketing of produce and in the purchase of equipment and supplies. Actual ownership of land is usually not affected, and in this way the agricultural cooperative differs from the collective farm. Agricultural cooperatives are often linked with cooperative banks and credit unions, which constitute another important type of cooperative. There is also cooperative activity in insurance, medical services, housing, and other fields.