Microsoft Policy Analyzer
I love group policy. I believe this is one of the main reasons why companies use Windows instead of an alternative OS like Linux or Mac OS. Group Policy gives you control over your environment, enabling, disabling, configuring, restricting and enforcing settings for the OS or any application you want. If a machine is on the domain, you know the settings will apply.
I provide Active Directory consulting very often and in most cases I have to troubleshoot Group Policy settings. This can prove challenging in some environments as the way they were created is not easy to grasp.
Microsoft just released (22 Jan 2016) a tool to help you analyse group policy settings. You can choose a group of policies and the tool will treat it as one, highlighting conflicts and duplication.
The tool is still in its early stages, but it is a great start. Find out more on the Microsoft Security Guidance blog: Policy Analyzer