There are many situations when you need to compare two AEM instances. The easiest approach is to compare packages, bundles and configurations. Here is how you can do it -    Compare package managers  http://localhost:4502/crx/packmgr/service.jsp?cmd=ls  Compare Bundles  http://localhost:4502/system/console/bundles.json  Compare Configurations  http://localhost:4502/system/console/status-Configurations  Compare system properties  http://localhost:4502/system/console/status-System%20Properties    You can then compare these manually using any text comparers.     Another quicker approach is to compare those using below tools by Aemstuff.com -      http://www.aemstuff.com/tools/cti.html  http://www.aemstuff.com/tools/coi.html           
My reflections on Digital Transformations - best practices, pitfalls etc etc...