By cooperation I mean simply joint effort through some formal or informal organization by otherwise separate churches or denominations. (religion-online.org)
Job clubs can be both formal and informal organizations formed with the purpose of providing members with assistance, support, and advice. (money-zine.com)
In America, Tocqueville observed, when citizens discerned new needs or purposes, they voluntarily formed committees or other informal organizations to meet them. (firstthings.com)