Unity API Versioner
This is an unofficial utility for Unity allowing you to search for which versions of Unity a method is available in.
It searches the dlls that comes with each Unity version, including UnityEngine.dll, UnityEditor.dll, UnityEngine.UI.dll and UnityEngine.Networking.dll. This tool automatically updates with new Unity releases on a daily basis.
If you have issues with the matched API not being what you intended it's likely that your search term was too ambiguous and matched multiple signatures in the API. Try fully qualifying the signature with the namespace.
This search tool matches against the declaring classes and ignores inheritance. While the "enabled" property is available on Rigidbody you should search for "Behaviour.enabled" as the Behaviour class declares the enabled property.