My favourite is Velocity. If you are using PHP Strorm, IntelliJ IDEA, Web Storm or other JetBrains software install Velocity from here: https://velocity.silverlakesoftware.com/ and install the plugin from the JetBrains' software from Preferences -> Plugins -> Browse repositories and search for "Dash";
After that install the docset sources from the program;
By choosing the word (method,object,class) select CTRL+SHIFT+D and you will get the documentation offline.