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 Keskühistu 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.