Coop Estonia Coop Estonia (previously ETK) is Estonia's oldest and biggest group in retail trade. (previously ETK) is Estonia's oldest and biggest group in retail trade. The Coop Eesti Kesk├╝histu or central association, which was established in 1917, offers a range of services to these cooperatives, from central logistics to cooperative marketing. It has always been owned by Estonian consumers and currently has nearly 70,000 client owners.