This is a extensive and well produced survey of world citizenship laws which was produced by Office of Personnel Management of the US government in 2000/2001, as a resource for dealing with multiple citizenship issues.
The directory provides a synopsis of the citizenship laws for 206 countries. It contains a wealth of information about multiple citizenship and the various ways that different countries approach it. The laws and rules of each country are individually summarized.
The directory provides an simplified overview, not a detailed legal analysis. It is a quick reference document focussed on some of the mechanics of citizenship, but it does not provide a complete picture of any of the countries listed, including the US itself. Keep in mind that citizenship laws, rules and interpretations are constantly changing, so some entries could be out of date. It is apparently not unusual to encounter differences between stated and actual practice in implementation of a country's citizenship laws.